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Tektronix 494P User's Manual

1. 4415 41 XGRAT 10 Specifies the X horizontal graticule size XCENT Is the X center of the display data in number of divisions relative to the left hand side of the graticule DXZERO Displays the X offset in divisions relative to XCENT DXMULT Displays the X multiplier XDIV Displays X divisions unit YGRAT 8 Specifies the Y vertical graticule size YCENT Is the Y center of the display in number of divisions relative to the bottom of the graticule DYZERO Displays the Y offset in divisions relative to YCENT DYMULT Displays the Y multiplier YDIV Displays Y divisions unit X Axis Scaling X axis specifications XGRAT XCENT DXZERO DXMULT and XDIV are used to interpret the position of the ordered points in absolute X values DXN DXMULT N PT OFF XDIV XCENT DXZERO where DXN is the X value in graticule divisions Y Axis Scaling Y axis specifications YGRAT YCENT DYZERO DYMULT and YDIV are used to interpret the position of the ordered points in absolute Y values DYN CYMULT VALN YDIV YCENT DYZERO where DYN is the Y value in graticule divisions VALN is the current data value DCOPY copy display query The DCOPY query response is the same as ID WFMPRE DPRE CURVE It allows transmission of information from one device to another in display units so that a hard copy can be made
2. Table 7 4 494P ERROR AND EVENT CODES Error Code Event Code Meaning 0 0 No error Command Errors Command header error Command argument error Missing argument Checksum error Bytecount error Input buffer overflow 103 illegal numeric format 109 END received in block binary 108 Binary block checksum error 103 illegal placement of question mark 101 Query not recognized 101 Header not recognized 106 End of message unit not expected arguments missing 103 Character argument not allowed for this header 103 Numeric argument not allowed for this header 103 String argument not allowed for this header 103 Binary argument not allowed for this header 103 Link not allowed for this argument 103 Special argument type not recognized 103 Special argument not allowed for this header 103 Character argument not recognized 150 input buffer overflow 7 11 System Commands and Queries 494P Programmers Error and Event Codes Table 7 4 cont Error Code Event Code Meaning Execution Errors 201 Command not executable in Local mode 204 Settings conflict 205 Argument out of range 206 GET Group Execute Trigger ignored not executed 250 Output buffer overflow remaining output lost 26 250 Output buffer overflow remaining output lost 27 201 Attempt to execute command in Local mode 28 205 FREQ TUNE FIRST or SECOND out of range t 29 205 FRQRNG out of range 30 205 CRES
3. 2 7 Source Handshake SH1 1 7 4050 Series Controller 2 7 Acceptor Handshake AH1 1 7 CP1100 and CP4100 Series Talker 18 2 2a ca seangNerd 1 7 Controllers 2 esse ese eves 28 Listener L3 n o oaran 1 7 9826A Controller uussa 2 8 Service Request SR1 1 7 Getting Smarter ai eae aa 2 8 Remote Local RL1 1 7 4050 Series Controller 2 8 Parallel Poll PP1 1 7 Device Clear DC1 1 7 Section 3 DEVICE DEPENDENT MESSAGE Device Trigger DT1 1 7 STRUCTURE AND EXECUTION Controller CO 56 1 7 Connecting to a rave IEEE IP 1 8 INBOGUCHON ets r epei aie Si Syntax Diagrams 5 3 1 Section 2 GETTING STARTED 39 input Messages ata ayes oe Input Message Format 3 2 Introduction 0 002 0008 2 1 Message Unit Delimiter 3 2 Setting and Querying Programmable Message Terminator TERM 3 2 CORUOIS res D LOrE EEEE ASERTA DA 2 1 Format Characters 3 2 Setting Programmable Controls 2 1 Input Buffering and Execution 3 2 4050 Series Controller 2 2 Command Format 3 2 CP1100 and CP4100 Series Header csi tec ae eaten we 3 3 Controllers 253 aes hte ag Werte 2 2 Header Delimiter SP 3 3 9826A Controller 2 2 Argument Delimiter 3 3 Summation 2 3 Argument Format 3 3 Mel 494P Programmers TABLE OF CO
4. A 10 Interface Functions and Messages A 11 IntrodUiCtlOnes scsi Peers eee A 114 RL Remote Local Function A 11 T TE and L LE Talker and Listener Functions A 11 SH and AH Source and Acceptor Handshake Functions A 12 DCL Device Clear Function A 12 DT Device Trigger Function A 12 C SR and PP Controller Service Request and Parallel Poll Functions 2466202 ahanekas in A 12 Taking Control Asynchronous or Synchronous 0005 A 13 Passing Control vee A 13 Performing a Serial Poll A 13 Performing a Parallel Poll A 13 Appendix B INDEX COMMANDS AND QUERIES v 494P Programmers vi LIST OF TABLES Table No 1 1 Bus Address aa ioen na nadaspa s aga 1 2 494P IEEE 488 Interface Functions 4 1 Front Panel Commands and Queries 4 2 Resolution Bandwidth Selection 4 3 Reference Level Settings 4 4 Calibration Codes 4 5 Display Control 2 eee eee eee 5 1 Display and Readout Data Mnemonics 6 1 Waveform Processing Commands and QUOI 4 ied ci Sid oun tere alee Sorelle eres 7 1 Device Dependent Commands and Queries 7 2 instrument Functions 0 2 7 3 TEST Conversion 000 e eee ee 7 4 494P Error and Event Codes 8 1 Execution Times 8 2 Transfer Times A 1 Major GPIB Interface Functions A 2 Interface Messages Referred to in this Appendix and Functions SS 4
5. INTO N LZ 220 GET Q FROM N TZ 230 PRINT Q 240 RETURN 9826A Controller O dim P 500 l oni 7 srq 2 eir7 3 ent enter message P Ar wrt 2 P 5 red z P 6 prt P 7 gto3 8 srq srds z rl 9 wrt z event 10 red z P Ll eir 7 iret Getting Started 494P Programmers ACQUIRING INSTRUMENT SETTINGS WITH SET The SET query enables the 494P to learn instrument settings both for reference and to be able to restore the instrument to those settings This query readies the instru ment to output a message that includes a response for each programmable function The format of the response allows it to be used to re store the instrument settings with no operator manipulation required First set up for the measurement and try it from the 494P front panel Store the message as it is transmitted by the 494P using the SET query Your controller must be ready for a long character string Dimension a string variable large enough for at least 500 characters for SET although the exact size depends on the current settings Then per form any desired instrument operations Finally restore the 494P to the original settings by transmitting back to the instrument the stored SET response A 4050 Series pro gram follows that steps you through the operation If you wish to transmit instrument settings from battery powered memory to a controller first recall the desired
6. OFF Normal steps are restored for reference level changes which cancels the A A mode if active NUM 1 equals ON numbers 0 5 are rounded to 1 Number 0 equais OFF numbers less than 0 5 are rounded to 0 Power up value Off Interaction This command along with VRTDSP con trols the analyzer response to REFLVL INC or DEC FINE fine reference level steps query 4415 147 Response to FINE query 4418 148 4 19 Front Panel Control 494P Programmers RLMODE PEAK RLMODE reference level mode command fies MDIST NUM i 4415 149 MNOISE The microcomputer is requested to assign gain distribution with minimum RF attenuation for a given reference level Generally this yields 10 dB less RF attenua tion than the MDIST argument and results in less displayed noise but may increase distortion MDIST Normal RF attenuation is requested for a given reference level Generally this yields 10 dB more RF attenuation than the MNOISE argument and results in lower signal levels in the analyzer hence less distortion NUM 0 equals MNOISE 1 equals MDIST and other numbers are rounded to 0 or 1 Power up value MDIST Interaction This command affects the gain distribu tion obtained with the REFLVL command see also MINATT and MAXPWR RLMODE reference level mode query ions O 4415 150 Response to RLMODE query MNOISE RLMODE SP pap 4415
7. 4 LIST OF ILLUSTRATIONS Figure No 8 4 A 1 A 2 A 3 A 4 A 5 B 1 Page The TEKTRONIX 494 Programmable Spectrum Analyzer 0000 x GPIB control and indicators 1 1 Status of active GPIB functions 1 2 Rear panel GPIB ADDRESS switches 1 2 Effect of message terminator switch for input and output o2 eS eacdaauieied serene 1 4 4924 controls used for data transfers 1 5 The rear panel IEEE STD 488 PORT GPIB 1 8 The 494P can be connected to a GPIB system in either a star A or a linear B configuration aoa cee eee eee 1 8 Front panel control commands and queries 4 1 Front panel Frequency Control commands 4 3 Front panel Frequency Span and Resolution COMMANDS aoc we nian ev were core a aes 4 10 Front panel Vertical Display and Reference Level commands 0eee eee 4 15 Front panel Sweep Control commands 4 24 Front panel Digital Storage Control COMMANAS asin Dads geet piel ag wes 4 28 Front panel Display Control commands 4 32 Front panel General Purpose commands and QUBIIOS 25 6 imi scabies dhruta NEE 4 34 Waveform Data related to the display 5 5 TEST Conversion Chart 00 7 10 Synchronizing controller and 494P for data ACQUISHION oc cae cee cere cee eee 8 3 A simple plot of a spectrum acquired from ae a a E TO E id oe deine are 8 6 How multiple use of the display data buffer is CONTONE oe hee a nee eee 8 8 Quote marks can be used in mess
8. but the most recent calibration attempt failed the last previously good value is used The value recorded for this item is the limit value i e the best it could do The actual required correction would exceed the limit 2 4 dB so this item is not calibrated This applies to level calibration only 4 The last calibration attempt for this item succeeded Front Panel Control 494P Programmers CAL FINE FINE fine reference level steps command C ON e 4415 146 ON Small steps are selected for the INC or DEC argu ments in the reference level command see REFLVL for de tails With vertical scale factors of 1 2 3 and 4 dB div FINE ON selects the A A mode A A Mode The A A mode is active when both FINE reference level steps and a scale factor of 4 dB div or less are selected In this mode the crt VERT DISPLAY readout initializes to 0 00 dB Changes in reference level are dis played as the difference between the initial level and the new level not the absolute reference level The initial gain distri bution RF attenuation and IF gain is not disturbed changes in reference level are created by an offset in the display This allows signals to be compared with inherently higher relative accuracy over a range of at least 0 dB to 48 dB from the initial level without an overload to the analyzer input This readout is available with UPRDO REFLVL returns the absolute reference level
9. 314 OSGIA Auenb ou aBueyo Aouenbay je uewesou ONIHSOOIL AIG AWIL nd ou 3YOLS lt LJIHS gt AIOQ NWdS AONSNDSYA d34aMs JI NIS 07 ANZ Vv SAVS NOILYOLSIC NIW SSION NIW HLGIMGNYS NOLLNTOS3Y 73437 SONSY3ASY inoavau Auanb ou SONILLSS T1VO3u Vv 3AVS lt LdIHS gt Y SAVS lt LdIHS gt YAHOLAYLS 3S71Nd LO1d lt idIHS gt Vad TWANVA NvdS XVW GOH XVW P NILIY 48 NIN Jamod yndu WwNUNXEN 4N3d daH wom Llwyd SONVY AONSNDAYS AONANOAYS YALNSD o11st sdajs Jeng souesaja4 JNIA YSXIW 1X3 lt LdIHS gt anb ou dSIG BYOLS lt LAIHS gt Asanb ou 77y93Y lt L4IHS gt NAOHIJY4 lt LJIHS gt AV K nd ou spo Buun sne6eq 4osund 39YYIJAV AYJd N10S34 LNNOO YSLNNOO Asanb ou 49 e LNNOD dd 3NN3SYE Wd lt idIHS gt Vv BAVS Y MIA upimpueq N0934 OLNV 440 NO 930 ONE WAN INIT AIAN DO7 MOYHYN IQIM J40 WNN 4X3 INIT LNI Nw gad 1X3 NYW 930 ONI OLNY WON WON XYW 930 ONI WON WNN 440 NO 4SIGW 3SIONW 930 ONE OLNY WNN 930 INI WNN 440 NO WON OlbidH LEdOML Z99 HL WAN 440 NO SONY 93G ONE WAN LNY a40 NO 440 NO 930 ONI WAN O30 ONI WAN 440 NO 440 NO 3d INI WAN WAN WAN 440 NO 440 NO av a v 340 NO 440 NO DAV Wad SONY WNN 440 NO 340 NO SOdA SOdH 907 dWY LNY a MIIA 340 NO dO NO 440 NO L g nb
10. 7 4 WAIT wait for end of sweep 7 4 REPEAT repeat execution 7 4 Status and Error Reporting 7 5 EOS end of sweep 7 5 RQS request service 7 5 Status Byte response to serial Pe EP OCTET OE AI ania naa 7 6 Section 7 Section 8 Page SYSTEM COMMANDS AND QUERIES cont Affect of Busy on Device Dependent Messages 7 7 Affect of Busy on Interface Messages 7 7 DT define triggered events 7 8 EVENT event information 7 8 ALLEV all events 7 8 NUMEV number of events 7 8 EVQTY event quantity 7 8 TEST internal test 7 9 Error and Event Codes 7 11 HELPS AND HINTS Introduction 0 ee eee eee 8 1 Data Acquisition 8 1 Synchronizing Controller and MOAR ows ncandrers TRAR NS 8 1 Synchronizing With the Sweep 8 2 Using the End of Sweep SRQ 8 2 INPUT An SRQ Alternative 8 2 Binary Waveform Transfer 8 4 Getting 494P Binary CURVE DUP bs 6 ese cone ee es ees 8 4 Sending a Binary CURVE to the AQIS en deiialed i Sinners ea tertee 8 4 Scaling Saving and Graphing Wave form Data euina eaa a 8 5 Saving the Scaled Array 3 8 5 Storing Settings 8 5 Waveform Plotting 8 5 Using PLOT 8 7 Multiple Use of Display Buffer for Wave form Processing and I O 8 7 Buffer Data Flow 8 7 Order Dependent Conf
11. CoE OOE O er POT O Om O Crapo LO na HO nnz JCO omen O EO TEO E aoe ef nnn Ls 4415 145 3 In the CAL response the same data is given in succes sion for the 1 MHz 100 kHz 10 kHz 1 kHz 100 Hz and 30 Hz filters in that order The center frequency and refer ence level accuracy calibration adjustment sequence is am plitude calibration horizontal position vertical position and log calibration The data given for each filter is the frequency error the frequency cal code the level error and the level cal code The frequency error is the difference between the mea sured filter frequency and 10 MHz expressed in Hz The level error is the difference between the measured filter level and the measured level of the 1 MHz filter expressed in dB Use Table 4 4 to decode the calibration code numbers Table 4 4 CALIBRATION CODES Code Number Description 0 A calibration value for this item has not been found i e this filter has never been calibrated before 1 The most recent calibration attempt failed the last previously good value is used 2 The value recorded for this item is the limit value i e the best it could do The actual required correction would exceed the limit 2 4 dB so this item is not calibrated This applies to level calibration only 3 A calibration value for this item has been found
12. S is called the sense bit and the three least significant bits PPP represent an octal number 0 through 7 that corresponds to a specific line on the data bus that an instrument must assert if its internal status has the same value as the sense bit S may equal 1 or 0 The actual parallel poii takes place after each instrument has been completely configured The concept is to have the controller receive one data byte that contains status in formation on all of the addressed instruments To receive this status byte the controller asserts the EOI line and the ATN line The assertion of EO may be coincident with ATN or later so long as both are asserted This may occur any time after the last PPE message The controller then reads the data bus lines while ATN and EO are asserted to inter pret the status of all selected instruments IEEE STD 488 GPIB System Concepts 494P Programmers To conclude the parallel poll the controller releases EOI and then ATN The instrument s does not need to be reconfigured for each subsequent parallel poll The PPU Parallel Poll Unconfigure command will clear all device con figurations and prevent them from responding to future polls The PPD Parallel Poll Disable command accom A 14 plishes essentially the same thing except that the PP func tion remains in the configured state PPU is a universal command all instruments while PPD is used with PPC and becomes an addressed command o
13. The sweep is triggered for pulsed signals by a signal with an amplitude of at least 1 0 V peak connected to EXT IN TRIG on the 494P rear panel NUM 0 equals FRERUN 1 equals INT 2 equals LINE and 3 equals EXT Numbers not equal to these values are rounded to the nearest valid integer Power up value Free run Interaction The signal frequency required for internal trigger is related to the center frequency In the frequency domain mode the required frequency corresponds to 1 2 division to the left of the left graticule edge in the time do main mode the required frequency is the center frequency In the frequency domain mode the required frequency must be within the selected band e g 1 7 GHz in band 2 Front Panel Control 494P Programmers TRIG TRIG triggering query Cie 4415 168 Response to TRIG query EXT mE 4415 169 4 25 Front Panel Controli 494P Programmers SIGSWP SIGSWP single sweep command 4415 170 On the first SIGSWP command the analyzer enters the single sweep mode which aborts the current sweep Once in the single sweep mode this command arms the sweep and lights the front pane READY light which remains lit for the duration of the sweep The analyzer makes a singie sweep of the selected spectrum when the conditions deter mined by the TRIG command are met Correction of the center frequency is done periodically and when SIGSWP is executed before the sweep
14. case if NUM exceeds the selection range it is rounded to the nearest end of the range No error message is issued Numbers within the range are rounded Units The 494P accepts arguments in engineering notation that is engineering units may be appended to a number argument The 494P microcomputer treats the combined number and units as scientific notation where the first letter of the units element represents a power of 10 K 1E 3 G 1E 9 and M 1E 3 or M 1E the value of M de pends on the function where MSEC stands for 1E 3 milli seconds in the TIME time div command and MHZ stands for 1E megahertz in the SPAN span div command Only the first letter of the units element is of importance the rest of the units element i e SEC or HZ does not contrib ute to the value of the command argument and can be omit ted Although more than one format character may precede the units only a space SP is shown in the command syn tax figures in this manual 3 3 Device Dependent Message Structure and Execution 494P Programmers Character Argument Arguments may be either words or mnemonics ON and OFF for instance are arguments for the commands that correspond to 494P front panel pushbuttons like Vertical Display or Digital Storage Link Argument The bottom path in the argument diagram combines both character and number arguments in a link argument The link is the colon which delimits the first and secon
15. domain XINCR TIME 100 for FULL in time domain XINCR TIME 50 for A or B in time domain N is the point number 0 1 2 3 PT OFF is graticule center for frequency domain transfers and left graticule edge for time domain transfers PT OFF 250 for A or B in frequency domain PT OFF 500 for FULL in frequency domain PT OFF 0 in time domain For example point 100 could have the following abso lute values XN 997 MHz for A or B with FREQ 1 GHz and SPAN 1 MHz XN 996 MHz for FULL with FREQ 1 GHz and SPAN 1 MHz XN 445 MHz for FULL with SPAN MAX XN 2 ms for FULL with SPAN 0 and TIME 2 ms Y Axis Scaling Y axis specifications YMULT YZERO and YOFF are used to interpret the data as the absolute value of the or dered data points YN YZERO YMULT VALN YOFF where YN is the value in YUNITS of point number N 5 3 Display Data and Crt Readout O 494P Programmers WFMPRE CURVE YZERO is the reference level in log vertical display mode and 0 in linear vertical display mode YMULT is the scale factor divided by 25 VALN is the unscaled integer data at point N YOFF is 225 top edge of graticule in log vertical dis play mode and 25 bottom edge of graticule in linear vertical display mode For exampie data value 125 graticule center could have the following absolute values YN 40 dBm at 10 dB div with a reference level of 0 dBm YN 0 112 V in linear mode with a reference leve
16. 151 4 20 PEAK peaking command 4415 152 AUTO During several sweeps the 494P micro computer automatically tunes the PEAK control to peak the largest signal in a window 1 division around the display data point The peak code that results is stored in battery powered RAM with a unique code retained for each band with the exception of the lowest frequency band in which peaking is not used These codes are used whenever AUTO PEAK is on Thus once a signal is peaked in a band signals at other frequencies in that band will be within a few dB of being peaked as well If a signal is not found within the 1 division window the previously acquired peaking code stored in battery powered RAM is used End of sweep in terrupts are not issued and triggering time division and the max hold digital storage parameters may be changed by the 494P while PEAK is being executed The previous param eters are restored when execution is complete Although this command uses digital storage it does not overwrite the A portion if SAVEA is ON The AUTO PEAK light is turned on NUM Numbers in the range 0 to 1023 set the value of the PEAK control and are stored in battery powered mem ory Non integers or numbers outside this range are rounded to the nearest integer in the range no warning is issued INC or DEC The value of PEAK is changed 1 from its current value and is stored in battery powered RAM KNOB The front panel M
17. 99 115 Internal error 0X1X010 1 37 53 101 117 Execution error warning j OxX1xX014140 38 54 102 118 Internal error warning LT status code 494P microcomputer busy condition Abnormal 1 normal 0 condition SRQ is asserted depends on RQS and EOS commands Power on is reported only if an internal switch is set to request this status Power on status This is set when the instrument is turned on only if an internal switch is set otherwise SRQ is not asserted at power up and power on status does not exist If selected by the switch this status cannot be masked by the RQS command The instrument is shipped with this switch off Refer switch selection to qualified ser vice personnel End of sweep status This is set when the 494P com pletes a sweep of the selected spectrum it indicates that digital storage has been updated Ordinary operation status This exists whenever there is no other status condition nothing out of the ordi nary to report Command error This occurs when a message cannot be parsed or recognized Execution error This results when a message is parsed and is recognized but cannot be executed such as FREQ 999 GHZ 7 6 Internal error This indicates that the 494P micro computer has discovered a malfunction that could cause the instrument to operate incorrectly Execution error warning This results from a com mand that the 494P executes but has a potential for er
18. CONTROLLER EXECUTION 130 amp 140 SEND FREQ I GHz SIGSWP WAIT FMAX POINT TO 494P 4 150 ADDRESS 494P TO TALK amp WAIT FOR 494P OUTPUT 4 INPUT 494P QUERY RESPONSE 494P EXECUTION BUFFER MESSAGE SET FREQ THEN START FIND MAXIMUM VALUE AND BUFFER QUERY RESPONSE OUTPUT QUERY RESPONSE 4415 18A Figure 8 1 Synchronizing controller and 494P for data acquisition REV FEB 1984 Helps and Hints 494P Programmers BINARY WAVEFORM TRANSFER Selecting binary rather than ASCil coded decimal speeds up waveform transfers Neither the controller nor the 494P has to perform a conversion between binary and ASCH The difference is evident in the times for both kinds of transfer listed in this section under Execution Times The gains possible by using binary are not hard to achieve Here s how Getting 494P Binary CURVE Output The 494P encloses binary waveform data values in some other items in the binary block format For details see the syntax diagrams in Section 5 For a 4050 Series routine that handles block binary en ter the following 500 REM GET 494P BINARY CURVE OUTPUT 510 DIM W 100 520 PRINT 37 0 37 255 255 530 PRINT Z WFMPRE ENC BIN CURVE 540 INPUT Z H 550 WBYTE 65 560 RBYTE A B W D 570 WBYTE 95 Line 520 Sets the second processor status byte in the 4050 Series controller to an alternate delimiter ASCII 37 T
19. Co l wrt z freq 100 mhz span l mhz refivl 20 dbm A 9826A device statement is used to assign z to the 494P on Os dev 2 701 The device statement assigns address 701 to z The 01 in 701 assumes the 494P GPIB ADDRESS switches are set to 1 but could be changed to any number between 00 and 30 Or z could be replaced in the write statement by 700 the 494P primary address The 9826A should be equipped with a GPIB Interface the General I O and Extended I O ROM and the String and Advanced Programming ROM to operate with the 494P ay l j Hf Summation Whatever controller is used or statement being sent the t actions shown in the following syntax diagram must be taken to get a message to the 494P ths sic nS RR EE 494P MLA MESSAGE m oe UNT amp UNL amp D r UNT amp UNL amp ATN ATN ATN ATN ATN The unlisten UNL and untalk UNT messages are op tional in the previous syntax diagrams of bus traffic How ever one or both are sent by most controllers when they begin transmitting and end transmitting on the bus in order to guarantee a clear communications channel The control ler sends the GPIB address you entered as part of the con troller s GPIB I O statement The controller either converts it to the 494P listen address or expects to receive the listen address with the offset included i e 32 The controller then sends the device dependent message
20. Data Flow Data flow through the buffer is diagrammed in Figure 8 3 This figure identifies the kinds of data operations as data paths or destinations branching from the right of the buffer The partitions in digital storage memory are shown as data sources or destinations branching from the left of the buffer 8 7 Heips and Hints 494P Programmers The WFMPRE and CURVE commands contain argu ments that set switches to control data flow through the buffer Either the CRVID argument or the WFID argument sets the switch to select A B or FULL A and B memory The ENCDG argument sets the switch that selects either ASCII or block binary waveform output Both switches are shown in their power up default positions They remain wherever they are set until changed by an appropriate com mand Order Dependent Conflicts Conflicts in the use of the buffer take place depending on the order in which waveform processing and I O occurs The CURVE query and display data point commands by con trast simultaneously load the buffer as they execute The CURVE command transfers the data to digital storage while executing and the display data point commands act on the data while executing The CURVE query by contrast does not transfer the data until after the entire message is exe cuted and the 494P receives its talk address Thus if these message units are mixed in a message the contents of the buffer may be changed between when it is loaded and
21. Definitions The interface control messages refer to Figure A 3 are sent and received over the data bus only with the ATN at tention line asserted true Interface message coding can be related to the ISO international Standards Organization A 6 7 bit code by relating data bus lines DIOt through DIO7 to bits B1 through B7 respectively in the Bits column of Fig ure A 3 Interface contro messages refer to Table A 2 include 1 the primary talk and listen addresses for instruments on the bus 2 addressed commands only instruments previ ously addressed to listen will respond to these commands 3 universal commands all instruments whether they have been addressed or not will respond to these commands 4 and secondary addresses for devices interfaced through a primary instrument Parallel Poll Enable PPE messages are derived from the characters in the first column under Lower Case letters in Figure A 3 decimal coded characters 96 through 111 The standard recommends the use of decimal code 112 lower case letter p for the Parallel Poll Disable PPD command All parallel poll configured instruments re spond with status information at the same time when the EOI line is asserted with ATN true ny i IEEE STD 488 GPIB System Concepts 494P Programmers B7 B6 B5 BITS B4B3B2B1 SBS 1 1 1 8 1 4 g 1 g 1 UPPER CASE 100 Of 120 40 64 50 P 16 80 LOWER CASE 1
22. I O buffer if preceded by a CURVE query in the same message This causes the que ried display data to be put back into digital storage A J CURVE display curve query EDO 4415 39 Response to CURVE query Gini OSB C ire FULL O BINARY suock N 4415 40 Display Data and Crt Readout 1 O 494P Programmers CURVE WAVFRM Waveform data is related to the display by Figure 5 1 DISPLAY UNITS REFERENCE LEVEL TOP OF CRT GRATICULE 200 250 300 350 400 450 500 100 200 300 400 500 600 700 800 900 1000 ARRAY POINT NUMBER A OR B 1 TO 500 FULL 1 TO 1000 4415 16 Figure 5 1 Waveform data related to the display WAVFRM waveform query evea 4415 33 The WAVFRM query response is the same as WFMPRE CURVE The most recent WFID and CRVID arguments select whether A B or both memories are se lected for data transfers and waveform processing in ASCII or binary numbers refer to both the WFMPRE and CURVE queries 5 5 Display Data and Crt Readout 1 O 494P Programmers DPRE DCOPY DPRE display preamble query CO 4415 34 DPRE elicits the transmission of the display preamble The display preamble contains numeric data items to be used with corresponding curves to reproduce a display Response to DPRE query 0 0 4 CO O GED O L 0 G O
23. ON The identify function is turned on Spurious con version products are shifted horizontally on alternate traces The trace is also offset vertically on alternate sweeps so true signals stand out OFF The identify function is turned off NUM 1 equals ON numbers gt 0 5 are rounded to 1 Number 0 equals OFF numbers less than 0 5 are rounded to 0 Power up value Off Interaction The span must be lt 50 kHz div in fre quency ranges 1 through 5 and lt 50 MHz div in frequency ranges 6 through 12 for the identify function to operate The SIGSWP commands cause alternating normal and vertically offset sweeps the first sweep is normal the next offset and so on IDENT identify query Goer 4415 135 Response to IDENT query IDENT SP eae Corr 4415 136 4 14 Front Panel Control 494P Programmers VERTICAL DISPLAY AND REFERENCE LEVEL Figure 4 4 The commands in this group control the vertical scale factor VRTDSP and reference level REFLVL and FINE of the display The microcomputer automatically selects the gain distribution combination of RF attenuation and IF gain according to the reference level mode RLMODE this takes into account the least amount of RF attenuation MINATT allowed or maximum power MAXPWR expected The microcomputer also automatically selects the peak PEAK analyzer response The pulse stretcher PLSTR stretches narrow or pulsed signals for acquisitio
24. REP 5 at the end causes the message to be executed a total of six times spanning down by two decades Helps and Hints 494P Programmers Spectrum Search Using REPEAT The 494P can perform a signal search by executing a loop in a single message and buffering the results without controller interaction The controller can later turn its atten tion again to the 494P and input the results The following routine works on a waveform in digital storage that is not updated during processing 100 REMARK SPECTRUM SEARCH 110 PRINT 2 POINT 0 120 PRINT Z RGTNXT POINT REPEAT 20 130 REMARK ts eeeeeeeere 140 REMARK INSERT ANY OTHER TASKS 150 REMARK t teeters cares 300 DIM P 20 2 310 INPUT 2 P Line 120 The 494P buffers the query responses as it executes the loop Line 310 Inputs the signal points as a string delimited by semicolons The number of query responses that can be buffered de pends on the query and the message sent to the 494P The buffer can handle 176 FRE REP 175 responses to the FREQ query which includes the frequency in scientific nota tion but the buffer can handle 293 PHS REP 292 of the shorter PHSLK query responses PHSLK ON or PHSLK OFF Messages and responses share buffer space Long messages will leave less space for responses than short messages 8 11 Helps and Hints 494P Programmers MESSAGES ON THE CRT USING RDOUT The 494P accepts either a single set or a double
25. XUNIT Identifies the horizontal display units either hertz or seconds YOFF Relates Y data to the Y origin by the Y offset YMULT Scales the Y values YZERO Points to the Y origin YUNIT Identifies the units that apply to the Y values either dBm or volts BN FMT RP Means each binary number single byte stands for a binary positive integer BYT NR 1 Means that binary numbers or ASCII coded digits are transferred as single bytes BIT NR 8 Indicates the precision max number of sig nificant bits of the binary numbers CRVCHK CHKSMO Specifies that the last byte of a binary transfer is a 2 s complement modulo 256 checksum for the preceding bytes except for the first byte which is a percent sign parser BYTCHK NULL indicates no byte check is appended to binary data transfers Display Data and Cri Readout 1 O 494P Programmers WFMPRE X Axis Scaling X axis specifications XINCR PT OFF and XZERO are used to interpret the position of the ordered points as abso lute X values XN XZERO XINCR N PT OFF where XN is the value in XUNITS on the X axis XZERO is the center frequency except in the follow ing cases XZERO 0 for time domain data ZEROSP XZERO frequency at graticule center for SPAN MAX XINCR is the absolute point to point distance on the X axis XINCR span div 100 for FULL in frequency domain XINCR span div 50 for A or B in frequency
26. able SPD message and optionally send the UNT message to release the last active talker Performing A Parallel Poll The Parallel Poll PP function provides an instrument with the capability to present one and only one bit of status information to the controller without being previously ad dressed to talk The parallel polling capability requires a commitment by the system program to periodically conduct a parallel poll sequence When an instrument responds to a parallel poll the single data bit presented to the controller may or may not indicate a need for service If the data bit is used as a service re quest indication the controller should perform a serial poll in order to obtain a complete status byte with more informa tion if the device has the SR function implemented Before an instrument can respond to a parallel poll the GPIB sys tem must first be configured In a typical sequence the con troller first sends an UNL command to clear the bus of listeners then the listen address of the device to be config ured Following this the controller sends the PPC Parallel Poll Configure command followed by a PPE Parallel Poll Enable message The PPE message contains coded in formation that tells the selected instrument which data line will carry the PP status bit for that device This entire se quence is repeated for each instrument to be configured The PPE message s sent by the controller has the form X110SPPP Bit 4
27. any other device dependent messages When it is finished executing the message the 494P is ready to handshake another mes sage which it then executes and so on You can depend on the 494P to assert NRFD on the GPIB while it is busy this prevents the execution of a controller GPIB output state ment that would send further instructions to the 494P For example enter 100 FOR I 1 TO 10 110 PRINT Z FREQ 31 GHZ 120 NEXT I Watch the 494P FREQUENCY readout change while this loop is executing You can see that the controller executes the loop more slowly than it would if line 110 only printed what is in quotes on the controller crt What is making the 4050 Series controller step through the loop at a more delib erate pace It must wait at line 110 after the first pass through the loop for the 494P to execute the previous FREQ command A controller GPIB input statement can also be used to synchronize the controller and the 494P The controller could make a table of frequency ranges for the frequencies covered by the previous loop filling the table only after the FREQ command is executed 100 DIM F 10 2 110 FOR I 1 TO 10 120 PRINT Z FREQ 1 GHZ FRQRNG 130 INPUT F I 1 140 F 1 2 I 1E 9 150 NEXT I 8 1 Helps and Hints 494P Programmers Line 130 Addresses the 494P to talk however the 494P does not begin talking until it finishes executing the message in line 120 This assures that the 494P u
28. button is pressed or the lt SHIFT gt PLOT sequence is performed Table 1 1 BUS ADDRESSES Primary Listen Talk Address Address Address 68421 0 0000 0 32 64 0 0001 1 33 65 0 0010 2 34 66 0 00141 3 35 67 0 0100 4 36 68 0 01041 5 37 69 00110 6 38 70 0011441 7 39 71 0 1000 8 40 72 0 1001 9 41 73 0 1010 10 42 74 010141 11 43 75 0 1100 12 44 76 0 1101 13 45 77 0 11410 14 46 78 me ar ce a 15 47 79 1 0000 16 48 80 1 0001 17 49 81 1 0010 18 50 82 1 00141 19 51 83 10100 20 52 84 1 0101 21 53 85 10110 22 54 86 PQ a Ae 23 55 87 1 1000 24 56 88 1 1001 25 57 89 1 1010 26 58 90 1610141 27 59 91 1 1100 28 60 92 EPIG 29 61 93 t pPrEFEg 30 62 94 SA ck a ee 31 UNL UNT Introduction to GPIB Operation 494P Programmers The address transmitted by the controller is seven bits wide The first five bits are the primary address and the last two bits determine whether it is a listen address 32 pri mary address or talk address 64 primary address For example 0100010 is primary address 2 a listener and 1000010 is primary address 2 a talker Secondary ad dresses when both bits 6 and 7 are set are not used by the 494P so are ignored Set the switches as desired but do not use 0 with 4050 Series controllers they reserve this address for themselves Selecting a primary address of 31 logically removes the 494P from the bus it does not respond to any GPIB ad dress but remains both unlistened and un
29. controller programs in this section extend beyond the column width limitations Where this occurs the overrun in formation is indented on the immediately following line Important whenever a line is broken it is always where a natural space occurs So be sure to add a space when inputting the program Table 5 1 DISPLAY AND READOUT DATA MNEMONICS Message Unit Function Waveform Transfers WFMPRE Selects A B FULL ASCII binary data transfers WFMPRE Requests waveform parameters from 494P CURVE Sends waveform data to 494P CURVE Requests waveform data from 494P WAVFRM Requests waveform parameters and data from 494P DPRE Requests display parameters from 494P DCOPY Returns model firmware version and options requests waveform and data parameters and display data Crt Readout Transfers RDOUT Sends one line of crt readout to 494P TEXT Selects SHORT LONG page for RDOUT TEXT Requests page size of RDOUT UPRDO Requests top line of crt readout from 494P LORDO Requests bottom line of crt readout from 494P Display Data and Crt Readout O 494P Programmers WFMPRE WAVEFORM TRANSFERS The 494P follows the Tektronix Interface Standard for GPIB Codes Formats Conventions and Features for waveform transfer Waveform transfers begin with a wave form preamble WFMPRE that identifies and scales the data and data CURVE that represents the waveform A command WAVFRM displays the responses to the WFM
30. either the adjustments need to be made or the automatic calibration will be done To recreate the front panel calibration function over the bus requires that five commands be sent to the instrument four for the adjustments and one for the automatic calibra tion The order of the first four adjustments is AMPL HPOS VPOS and LOG User prompt messages are displayed on the crt screen Since the 494P is in the Remote mode the controller keyboard must be used to go to the next adjust ment step A device clear is sent to the 494P to terminate the execution of each adjustment command Note that HPOS could be deleted without affecting the other adjust ments but the others should be done in the recommended order The program must contain a message instructing the operator to connect the calibrator 8 12 100 PRINT Z RDO CONNECT CAL OUT TO RF INPUT 110 PRINT Z RDO HIT RETURN AFTER COMPLETING EACH STEP 120 INPUT B 130 PRINT 2 CAL AMPL 140 INPUT B 150 WBY 20 160 PRINT Z CAL HPOS 170 INPUT B 180 WBY 20 190 PRINT Z CAL VPOS 200 INPUT B 210 WBY 20 220 PRINT Z CAL LOG 230 INPUT B 240 WBY 20 250 PRINT Z CAL AUTO 1 j Helps and Hints 494P Programmers COMPARING THE STATUS BYTE AND THE ERR EVENT RESPONSE The 494P status byte and ERR EVENT responses de scribed in Section 7 play complementary roles in GPIB sys tem programming The status
31. existance of two conditions can cause CURVE data output commands to be invalid 1 if CURVE is followed by a command to update the display data point and 2 if digital storage is updated during the execution of the message either by repetitive sweeps or by the SIGSWP command When both of these conditions exist the curve data out put that follows completion of the entire message will not be the data that was loaded in the buffer at the time CURVE was executed Instead the curve data that is output will be the data that was loaded by the later command to update the display data point because this later data overwrites the data already loaded in the buffer at the time CURVE was executed The curve data is output as expected if CURVE follows the command to update the display data point in stead of preceding it because no conflict occurs in the way the commands use the buffer b If CURVE is preceded by a command to update the display data point the display data output commands may be invalid In this case the curve data is loaded into the buffer as it is received from the GPIB but it is over written when the display data point is updated 6 3 Waveform Processing 494P Programmers CENSIG TOPSIG This overwriting causes the data already loaded into the buffer from digital storage to be written back into digital storage when the CURVE command is then exe cuted with the updated data The overwriting also causes the curv
32. factor 0 25 dB 3 dB A A mode Equal to VRTDSP scale factor 0 25 dB 2 dB A A mode 1 dB 0 25 dB 1 dB A A mode 1 dB 0 25 dB LIN 1 dB Either 6 dB or 8 dB varies to match 1 2 5 volts div sequence Power up value 30 dBm Front Pane Controi 494P Programmers REFLVL REFLVL reference level query REF C 4415 141 Response to REFLVL query Er j 4415 142 The value returned is the absolute reference level whether or not in the A A mode 4 17 Front Panel Control 494P Programmers CAL CAL cal command eect et NUM D 4415 143 To request the 494P to perform an internal calibration input the following program RQS O CAL ERR RQS 1 NUM 0 equals AUTO 1 equals LOG 2 equals AMPL 3 equals HPOS and 4 or higher equals VPOS CAL without arguments or CAL AUTO The resolu tion bandwidth filter frequencies are calibrated with respect to 10 MHz and levels relative to the 1 MHz filter level within a range of 2 4 dB During operation the word CALI BRATING appears on the screen CAL LOG The instrument is set up to enable the oper ator to adjust the front panel LOG CAL control CAL LOG has an indeterminate execution time and will operate until either a device clear DCL is received via the GPIB port or the 494P is returned to local control via the instrument front panel An instruction message appears on the screen CAL AMPL The instrument is
33. functions Frequency NOTE Frequency span and resolution Vertical display and reference level Sweep control Digital storage Display control General purpose Some of the lines of input in examples of controiler programs in this section extend beyond the column width limitations Where this occurs the overrun in formation is indented on the immediately following line Important whenever a line is broken it is always where a natural space occurs So be sure to add a space when inputting the program gt i D g C E ektrdnit 494p SERE ene lt 4G TENSITY Dee REFERENCE 40 i oO FREQUENCY es FREQUENCY SPAN and RESOLUTION V DIGITAL STORAGE O VERTICAL DISPLAY and REFERENCE LEVEL A DISPLAY CONTROL g SWEEP CONTROL GENERAL PURPOSE 4415 08 Figure 4 1 Front panel control commands and queries Front Panel Control 494P Programmers The mnemonics in Table 4 1 correspond to the 494P commands for front panel controls and related functions Table 4 1 FRONT PANEL COMMANDS AND QUERIES Table 4 1 cont Identification identification Control Mnemonic Number Control Mnemonic Number O Frequency g Sweep Control CENTER FREQUENCY FREQ 1 amp FREQ ENTRY TUNE 2 PER RUN 1ST Loe FIRST 2ND Loe SECOND es TRIG 25 Disable Tuning Corrections lt SHIFT gt DISCOR eae ce FREER
34. instrument s designer it is not likely that one single in strument will have all ten interface functions For example an instrument generally doesn t need to implement the Par allel Poll PP function if the instrument can respond to a serial polling sequence from the controller in charge of the GPIB system The following discusses the interface functions and their relationship to the interface control messages shown in Fig ure A 3 All the interface control messages discussed are sent and received over the GPIB with the ATN line asserted low RL Remote Local Function The RL function provides an instrument with the capabil ity to select between two sources of input information This function indicates to the instrument that its internal device dependent functions are to respond to information input from the front panel Local or to corresponding program ming information from the GPIB Remote Only the system controller is permitted to assert the REN Remote Enable line whether or not it is the controller in charge at the time When the system controller asserts the REN line an in strument on the GPIB goes to a remote mode when it is addressed as a listener with its listen address not before An instrument remains in a remote mode until the REN line is released high or an optional front panel switch on the instrument is activated to request the local mode or a GTL Go To Loca command is received while the instrument
35. is enabled as a listener However the controller can disable the instrument s front panel return to local switch es by sending a LLO Local Lockout command The LLO command must be pre ceded or followed by a listen address MLA to cause the instrument to go to a remote mode with front panel lockout The UNL Unlisten command does not return an instrument to the local mode When the REN line goes false it must be recognized by all instruments on the bus and they must go to the local mode within 100 us If data bytes are still being placed on the bus when REN goes false the system program should assure that the data bytes are sent and received with the knowledge that the system is in a local mode not remote T TE and L LE Talker and Listener Functions NOTE Although discussed under one heading the T TE and L LE functions are independent of each other The T Talker and TE Talker Extended functions pro vide an instrument and its secondary devices if any with the capability to send device dependent data over the GPIB In the case of a controller the capability to send device dependent program data over the GPIB The Talker T function is a normal function for a talker and uses only a one byte primary address code called MTA My Talk Ad dress The Talker Extended TE function requires a two byte address code an MTA code followed by the second byte called MSA My Secondary Address Only one instrument in t
36. is changed gt 1 GHz to improve amplitude accuracy FREQ center frequency query 0O 4415 91 Response to FREQ query CORONES 4415 92 4 4 TUNE incremental frequency change command a some A ie 4415 93 NUM The analyzer changes its center frequency by using the value of the command argument as an offset to its previous center frequency There is no TUNE query Eni Rs 2 aa FIRST 1st LO frequency command OH 4415 94 NOTE The FIRST and SECOND commands are included pri marily to allow the SET response to exactly re create the 494P settings NUM The 494P 1st LO is set to the requested fre quency The resulting center frequency will be displayed Power up value 2072 MHz FIRST ist LO frequency query Crier 4415 95 Response to FIRST query 4415 96 Front Panel Controi 494P Programmers FIRST SECOND SECOND 2nd LO frequency command EE n 4415 97 NOTE The FIRST and SECOND commands are included pri marily to allow the SET response to exactly re create 494P settings NUM The 494P 2nd LO is set to the requested fre quency The resulting center frequency will be displayed Power up value 2182 MHz SECOND 2nd LO frequency query om O 4415 98 Response to SECOND query 6D NRI je 4415 99 4 5 Front Panel Contro l 494P Programmers DISCOR FRORNG DISCOR disable frequency corrections com
37. mode is turned on OFF The counter mode is turned off NUM 1 equals ON numbers 0 5 are rounded to 1 Number 0 equals OFF numbers less than 0 5 are rounded to 0 When no argument is included an immediate signal count occurs whether or not the counter mode is on no change occurs in the ON OFF status of the counter mode Power up vaiue Off COUNT counter query Se ingo Response to COUNT query 4415 108 The number returned in this response is the result of the last count regardiess of whether COUNT is ON or OFF Front Panel Control 494P Programmers COUNT CRES CNTCF CRES counter resolution command He ye ores JGP nu NUM S 4415 109 NUM The proper decade of counter resolution is se lected for use Numbers that are not powers of ten will be set to the next lower power of ten up to a maximum of 1 GHz resolution Power up value 1 Hz CRES counter resolution query O 4415 110 Response to CRES query CRES SP NAS CNTCF count to center frequency command 4415 111 A count of the signal is taken at center screen then this signal count result is transferred to the center frequency This tunes the 494P to the signal counted Accuracy is lim ited by the count resolution in use when the signal count is done There is no CNTCF query 47 Front Panel Control 494P Programmers DELFR DEGAUS DELFR A frequency command CEDEO ot 4415 112 ON The A freq
38. of the display ETNON 4415 42 Display Data and Crt Readout 1 O 494P Programmers RDOUT TEXT CRT READOUT TRANSFERS Readout messages RDOUT can be displayed on the screen in either a 2 line or a 16 line mode TEXT Two crt readout queries return the upper row of normal readout characters UPRDO or the lower row LORDO RDOUT readout message command CHARACTER J mm CHARACTER HO ay ms 4415 43 oor GAC CHARACTER In the TEXT SHORT mode the spec tral display remains on the crt the readout is cleared and the first 40 ASCil coded characters are displayed across the bottom of the 494P crt When the RDOUT command sends a new line of characters it is entered at the bottom of the crt and the previous bottom line of characters is moved to the top of the crt Each succeeding line of characters is displayed at the bottom of the crt and the previous bottom line moves to the top discarding the previous top line Thus each new RDOUT command causes the 494P readout to scroll Lower case characters are displayed as upper case characters In the TEXT LONG mode the screen is completely blanked and the first 40 remotely entered characters are displayed in the 1st line at the top of the crt screen Successive lines of characters are entered on the following lines until the 16th bottom line is reached Then as each successive line of characters is entered the entire screen scrolls up one line
39. on the slowest instrument involved in the handshake RFD means Ready For DATA DAC means Data Accepted JEEE STD 488 GPIB System Concepis 494P Programmers NDAC Not Data Accepted Each assigned listener holds the NDAC signal line asserted until the listener accepts the data byte currently on the bus When ail assigned listeners have accepted the current data byte the NDAC signal line becomes unasserted high telling the talker to remove the data byte from the bus The DAC message Data Accepted tells the taiker that ail assigned listeners have accepted the current data byte NOTE One handshake cycle transfers one data byte then the listeners reset the NRFD line high and the NDAC line low before the talker asserts DAV for the next data byte transfer Both NRFD and NDAC high at the same time is an invalid state on the bus Management Bus The management bus is a group of five signal lines that are used to control the operation of the IEEE Std 488 GPIB Digital Interface IFC Interface Ciear The system controller is the only instrument on the bus allowed to assert IFC IFC is asserted for gt 100 us to place all instruments in a predetermined state While IFC is being sent only the DCL Device Clear LLO Local Lockout PPU Parallel Poll Unconfigure and REN Remote Enable interface messages universal com mands will be recognized ATN Attention The controller in charge is the only in strument on the bus al
40. on unlocking of 1st LO 354 Calibration failure 355 Battery powered RAM checksum error 382 1st LO tuning system failed 383 1st LO tuning system recovered from a failure 386 2nd LO tuning system failed 387 2nd LO tuning system recovered from a failure 388 Phase lock system failed 389 Phase lock system recovered from a failure 396 Power supply out of regulation 397 Power supply regained regulation 398 Frequency reference unlocked 399 Frequency reference relocked 350 Tuning DAC carry operation failed 351 Failed to lock 1st LO 352 Lost 1st LO lock 353 Recentering failure on unlocking of 1st LO 354 Calibration failure 355 Battery powered RAM checksum error 382 1st LO tuning system failed 386 2nd LO tuning system failed 388 Phase lock system failed 394 IF count failed 396 Power supply out of regulation 398 Frequency reference unlocked 383 tst LO tuning system recovered from a failure 387 2nd LO tuning system recovered from a failure 389 Phase lock system recovered from a failure 395 IF count recovered from a failure 397 Power supply regained regulation 399 Frequency reference relocked System Events 401 Power on 402 Operation complete 97 401 Power just came on 98 402 Operation complete end of sweep Internal Error 99 302 Unrecognized event occurred 7 13 J of Section 8B 494P Programmers HELPS AND HINTS INTRODUCTION This section covers some techniques for programming the
41. operation is com plete Only after completing the operation can the instru ment repeat its basic operation in response to the next GET message Thus the basic operating time is the major factor that determines how fast the instrument s can be repeat edly triggered by commands from the bus C SR and PP Controller Service Request and Parallel Poll Functions The C Controller function provides the capability to 1 send primary talk and listen addresses secondary ad dresses universal commands and addressed commands to all instruments on the bus 2 respond to a service request message SRQ from an instrument 3 or to conduct a par allel poll routine to determine the status of any or ail instru ments on the bus that have the Parallel Poll PP function implemented If an instrumentation system has more than one control ler only the system controller is allowed to assert the IFC Interface Clear and REN Remote Enable lines at any time during system operation This is true whether or not it is the controller in charge at the time if a controller requests system control from another con troller and it receives a message from another controller to send REN the system controller must verify that the REN line remains unasserted false for at least 100 xs before asserting REN The time interval that REN is asserted de pends on the remote programming sequence and will vary with the program The IFC line must be assert
42. out of range 31 205 SPAN out of range 32 205 RESBW out of range 33 205 MAXPWR or MINATT out of range 34 205 REFLVL out of range 35 205 VRTDSP LIN out of range 36 205 VRTDSP LOG out of range 37 205 TIME out of range f 39 204 IDENTIFY not allowed in this span div hd 40 204 Signal finds not allowed in this span div 45 206 GET Group Execute Trigger ignored not executed 46 205 NUMEV out of range 47 205 STORE RECALL DSTORE or DRECAL out of range 48 204 PHSLK cannot be turned OFF ON directly with PHSLK command Execution Warnings 550 FREQ change caused EXMXR change 551 SPAN defaulted to MAX a 552 SPAN defaulted to 0 553 UNCAL light turned on aa 554 UNCAL light turned off 555 Multiple use of display buffer 49 550 FREQ change caused EXMXR change 50 551 SPAN defaulted to MAX 51 552 SPAN defaulted to 0 52 553 UNCAL light turned on 53 555 Multiple use of display buffer 54 554 UNCAL light turned off Internal Warnings 650 Frequency reference changed to INT 651 Frequency reference changed to EXT 55 650 Frequency reference changed to INT 3 56 651 Frequency reference changed to EXT 7 12 oq System Commands and Queries 494P Programmers Error and Event Codes Table 7 4 cont Error Code Event Code Meaning Internal Errors 302 System error 350 Tuning DAC carry operation failure 351 Failed to lock 1st LO 352 Lost tst LO lock 353 Recentering failure
43. overload at the ex pected maximum power level The microcomputer selects a minimum RF attenuation so that the NUM signal level is reduced to 18 dBm at the 1st Mixer This is the ana lyzer s 1dB compression point The maximum non destructive power level that can be connected to the RF INPUT is 30 dBm INC or DEC The minimum RF attenuation is changed to the next higher or lower step if any Interaction The range of RF attenuation is limited in response to the REFLVL command which limits the range of the REFLVL command MAXPWR cancels the previous limit set by either MINATT or MAXPWR MAXPWR maximum input power query ire 4415 159 Response to MAXPWR query 4415 160 4 22 PLSTR pulse stretcher command 4415 161 ON The fall time of detected signals is increased so very narrow pulses in a line spectrum display can be seen The effect is apparent for signals analyzed at resolution bandwidths that are narrow compared to the span It may be necessary to turn on the pulse stretcher for digital stor age of such signals especially if the cursor is set high enough to average them Pulse stretcher may be required to view or store fast pulsed signals For short pulses the signal may exist for less time than is required for a point to be digitized causing either no value or too low a value to be stored OFF The pulse stretcher is turned off NUM 1 equals ON numbers gt 0 5 are rounde
44. range 1 to 1000 would be searched Interaction See Display Data Point Commands Interaction FMIN find minimum value command Cm es ee jC non 4416 31 This routine sets the display data point to the point in digital storage with the smallest Y value If the smallest Y value is located at more than one point the first left most point is acquired The optional arguments are two display X values The FMIN command will limit its search over this X range otherwise the full X range 1 to 1000 would be searched Waveform Processing 494P Programmers FMAX FMIN Display Data Point Commands Interaction 1 The preceding waveform processing commands oper ate only on the waveform specified by the last WFMPRE or CURVE command either A or B or full both A and B The waveform involved is first copied into a buffer If the wave form is only haif resolution either A or B it is duplicated in the buffer to make a full 1000 point waveform before pro cessing Thus whether the command operates on A or B or both the range of X values for the display data point is always 1 to 1000 2 The preceding waveform processing commands that update the display data point use the same buffer memory as display data I O therefore commands for these two functions can interact if executed as part of the same mes sage This command interaction can cause invalid data out put with either CURVE or CURVE a The simultaneous
45. response characters are shown exactly as they will be returned Boxes are used for defined elements and contain a name that stands for the element defined elsewhere NUM is such an name and is defined under Numbers Elements of the syntax diagram are connected by arrows that show the possible paths through the diagram i e the sequence in which elements must be transferred Parallel paths mean that one and only one of the paths must be followed while a path around an element or group of elements indicates an optional skip Arrows indicate the direction that must be fol lowed usually the flow is to the right but if an element may be repeated an arrow returns from the right to the left of the element Some examples of such sequences follow Gb 4415 49 3 1 Device Dependent Message Structure and Execution 494P Programmers 494P INPUT MESSAGES A remote control message to the 494P comprises one or more message units of two types The message units either consist of commands that the 494P inputs as control or measurement data or they consist of queries that request the 494P to output data One or more message units can be transmitted as a mes sage to the 494P Message units contain ASCII characters binary may also be used for waveforms The 494P accepts either upper case or lower case characters for the mnemon ics shown in the syntax diagrams Input Message Format 4415 50 Message Unit Delimi
46. selected a resolu tion bandwidth to go with a span of the selected 1 MHz What is that bandwidth The query RESBW readies the 494P to output the answer The query can be inserted in any message to the 494P It is executed in its turn This means that if RESBW precedes the SPAN command in the previous example the 494P in forms you of the old rather than the new resolution band width More than one query can be contained in a message to ask for both resolution bandwidth and for instance whether a video filter is on Just add these queries into the message used in the previous example and combine the message with the controller GPIB input statement 2 3 Getting Started 4S84P Programmers 4050 Series Controller 100 PRINT Z FREQ 100 MHZ SPAN 1 MHZ REFLVL 20 DBM RESBW VIDFLT 110 INPUT Z2 P 120 PRINT P If a query or command that has a lengthy return e g CURVE HELP SET WFMPRE is included as part of this program character string P must be dimensioned large enough to accommodate the message CP1100 and CP4100 Series Controllers 100 PUT FREQ 100 MHZ SPAN 1 MHZ REFLVL 20 DBM RESBW VIDFLT INTO N LZ 110 GET P FROM N TZ TZ is the 494P talk address derived in the same manner as LZ i e primary address 64 UNT amp UNL amp ATN ATN 9826A Controller l1 wrt z freq 100 mhz span 1 mhz reflvi 20 dbmsresbw vidflt 2 red 2 P With the 9826A you must dimensio
47. set of quote marks to delimit the crt message With 4050 Series controllers use a single set of quotes around the message inside the RDOUT command 100 PRINT Z RDOUT SET THE PEAK AVERAGE KNOB This is necessary because the 4050 Series controller uses a double set of quotes to set off the message following the colon in the PRINT statement A variation gets around this if you want quote marks to appear on the 494P crt 100 PRINT Z RDOUT PRESS RETURN TO LOCAL The controller strips off the first set in each double set of quote marks and transmits the second set of each double set for the display as shown in Figure 8 4 The RDOUT message continues to be displayed if the 494P remains under remote control To demonstrate the above messages by themselves add the statement 110 GOTO 110 To scroll the RDOUT message to the top of the 494P screen insert 105 PRINT Z RDOUT PRESS RETURN TO LOCAL Figure 8 4 Quote marks can be used in messages on the 494P ert USING CAL OVER THE BUS The CAL function activated from the front panel does two things It directs the operator in the adjustment of the four screwdriver adjustments AMPL and LOG CAL and Vertical and Horizontal POSITION CAL also performs an automatic calibration of the relative amplitudes of the reso lution bandwidth filters The CAL command allows these functions to be separated so that
48. settings then execute the SET sequence that follows 4050 Series Controller Here is a 4050 Series BASIC program that allows you to store two instrument set ups by pressing User Definable keys Only keys 1 and 2 are used in this program but oth ers could be used in a similar manner To restore the set ups simultaneously press SHIFT and the key used to store the settings NOTE Be sure to use the same line numbers we used in the example for all input messages on lines 1 through 50 Many of the line numbers directly relate to the special characteristics of the 4050 Series User Definable keys refer to the 4050 Series Operators manual for more information Also portions of this main program will be expanded for use in Acquiring A Waveform later in this section Save this program as it is here for Jater use 2 6 1 REMARK SETTINGS PROGRAM 2 G0 TO 100 4 K l 5 GOSUB 1000 6 RETURN 8 K 2 9 GOSUB 1000 10 RETURN 44 K 1 45 GOSUB 2000 46 RETURN 48 K 2 49 GOSUB 2000 50 RETURN 100 DIM K 500 110 DIM L 500 120 SET KEY 130 GO TO 130 1000 REMARK LEARN INSTRUMENT SETTINGS 1010 PRINT 494P SETTINGS NOW LEARNED 1020 PRINT Z SET 1030 GO TO K OF 1040 1060 1040 INPUT Z K 1050 GO TO 1070 1060 INPUT Z b 1070 RETURN 2000 REMARK RESTORE INSTRUMENT SETTINGS 2010 PRINT 494P SETTINGS NOW RESTORED 2020 GO TO K OF 2030 2050 2030 PRINT 2Z K 2040 GO TO 2060 2050 PRINT Z L 206
49. the enabled talker and the enabled listeners on the three line data transfer control bus transfers one data byte eight bits at a time These data bytes are sent and received in a byte serial bit parallel fashion Since the handshake sequence is an asychronous opera tion no clock signal on the bus the data transfer rate is only as fast as the slowest instrument involved in a data byte transfer A talker cannot place data bytes on the bus faster than the slowest listener can accept them Figure A 4 illustrates the flow of data bytes on the bus when a typical controller sends ASCH data to an assigned listener The first data byte decimal 44 enables an instru ment at address 12 as a primary listener The second data byte decimal 108 is optional for example enabling a plug in device at secondary address 12 as the final destination of the data to follow The data is the two ASCII characters A and B decimal 65 and decimal 66 Note that the ATN line is asserted for the first two data bytes and unasserted for the device dependent character to indicate the last data byte in the message A 8 The controller activates the ATN line again and sends the universal unlisten UNL and untalk UNT commands to clear the bus Six handshake cycles on the data transfer control bus are required to send the six data bytes Transfer Bus Handshake Each time a data byte is transferred over the data bus an enabled talker and all enabled listener
50. when it is acted on or transferred Here is an example combining both CURVE output and input in the same message this is a way to talk to yourself 100 REMARK WRONG WAY 110 DIM B 1000 120 PRINT Z CURVE CURVE 3A 130 INPUT Z B DISPLAY DATA WAVEFORM BUFFER i l DIGITAL STORAGE Pi p e a A l curve CRVID WFMPRE WFID This program attempts to obtain a 494P waveform and replace it with a waveform residing in controller array A But that s not what happens The 494P does buffer the CURVE data transmitted from array A by line 120 but then the 494P overwrites the data in the buffer when it executes the mes sage in line 120 This occurs because the CURVE query is executed first transferring the contents of digital storage to the buffer When the 494P executes the CURVE command that follows it writes the contents of the buffer back into digital storage As a result the controller gets the digital storage waveform it requested and stores it in array B as it executes line 130 However the data from array A is lost and does not replace the original digital storage waveform Instead of the previous example try 100 REMARK RIGHT WAY 110 DIM B 1000 120 PRINT Z CURVE 130 INPUT 2 B 140 PRINT Z CURVE 5A Line 120 Requests a curve which the 494P buffers Line 130 Inputs the curve before it is overwritten by line 140 The semicolons enclosing A at the end of line 140 in struct
51. 0 RETURN 2070 END Lines 4 through 50 Call subroutines when 4050 Series User Definable keys 1 or 2 are pressed They set a param eter to indicate whether you are asking for learn string 1 or 2 then jump to subroutines that perform the transfer of settings to or from the 494P Lines 100 through 130 Exercise the subroutines dimen sion the string variables and arm the User Definable keys SET KEY During the idle time established by line 130 the controller waits for the first input of settings from the 494P Lines 1000 through 1070 Input a SET response from the 494P and stores it Lines 2000 through 2060 Return a SET response to the 494P RESETTING THE 494P AND INTERFACE MESSAGES The INIT command resets the 494P programmable con trols to their power up state see Section 7 for more on this command INIT is sent in the same manner as other commands Interface message DCL clears the 494P I O buffers and can be used to restart bus communications with the ana lyzer DCL does not interrupt message execution except for the WAIT command If the 494P is waiting for its talk ad dress so it can execute an output query output is aborted and the buffers are cleared by DCL decimal code 20 or any device dependent input The decimal codes for other universal commands are 17 for LLO local lockout 21 for PPU parallel poll unconfigure 63 for UNL unlisten and 95 for UNT untalk For addressed commands such as GTL
52. 110 ON SRQ THEN 200 120 PRINT Z SIGSWP E0S ON a 130 FOR I 1 TO 5 140 PRINT Z FREQ I GHZ SIGSWP 150 WAIT 160 PRINT Z FMAX POINT 170 INPUT Z P I 180 NEXT I 200 POLL Q1 Q232 A 210 RETURN Mae With no WAIT command following SIGSWP in line 140 the 494P is ready to buffer another message But the con troller does not send it immediately because of the WAIT statement in line 150 The SRQ that the 494P asserts at the end of its sweep which was enabled in line 120 triggers the controller to perform a serial poll lines 200 and 210 and then send the message in line 160 INPUT An SRQ Alternative An INPUT statement in the right place is an alternative to waiting for an end of sweep SRQ This tactic takes advan tage of a 494P output feature if the analyzer has no output when it receives its talk address it outputs a byte with all bits set to one as soon as it is not busy 100 DIM P 5 110 PRINT Z SIGSWP 120 FOR I 1 T0 5 130 PRINT Z FREQ I GHZ 140 PRINT Z FREQ 1 GHZ SIGSWP WAIT 150 INPUT Z D 160 PRINT Z FMAX POINT 1 170 INPUT Z P I 180 NEXT I Here the WAIT is put back into the 494P message and the INPUT statement in line 150 stalls the controller while the 494P makes a sweep D serves the purpose of a dummy string the data is not input until fine 170 Helps and Hints 494P Programmers 4050 SERIES
53. 15 423 Response to ZEROSP query Ca COMO D The response is the current zero span condition 4415 124 NOTE it is recommended that ZEROSP be used rather than SPAN 0 Enabling ZEROSP turns on the front panel indicator that provides positive indication that the zero Span mode is set in addition to the readout Then when ZEROSP is turned off the previous SPAN DIV setting is restored 4 11 Front Panel Controi 494P Programmers MXSPN RESBW MXSPN max span mode command ON ees 4415 125 ON The 494P sweeps the entire range of frequencies in the current FRQRNG FREQ no longer corresponds to center frequency it now corresponds to the frequency at the tunable marker on the 494P display ON saves the previ ous FREQ SPAN DIV which is restored when MXSPN is OFF OFF MXSPN ON is cancelled leaving the FREQ SPAN DIV at the previously selected value NUM 1 equals ON numbers 0 5 are rounded to 1 Number 0 equals OFF numbers less than 0 5 are rounded to 0 Power up value Off Interaction When the SPAN setting is changed MXSPN is turned off MXSPN max span mode query O Response to MXSPN query Con OFF The response is the current max span condition 4415 126 4415 127 NOTE it is recommended that MXSPN be used rather than SPAN MAX Enabling MXSPN turns on the front panel indicator that provides positive indication that the max span mode is set in addition to the re
54. 40 60 16 we Bi snes 4 121 A at 51 Q 17 81 161 q 7 42 52 R 18 82 103 123 c 53 S 19 83 124 54 T 20 84 21 85 u 75 v 76 w x 25 y 121 172 26 422 74 3c 27 123 28 124 75 3D m 6D 109 a 12 76 3 gt 4E 78 SE 94 156 14 n 6E 110 7E 126 15 H us 34 47 77 oF 63 45 137 0 UNT 4F 79 SF 95 15 o 6F ut 177 DEL RUBOUT 7F 127 ADDRESSED UNIVERSAL COMMANDS COMMANDS LISTEN ADDRESSES TALK ADDRESSES octal j25 PPU NAK 5 2 hex ft 1 decimal GPIB code ASCII character Figure A 3 ASCII amp GPIB Code Chart SECONDARY ADDRESSES OR COMMANDS REF ANSI STD X3 4 1977 IEEE STD 488 1978 ISO STD 646 1973 4415 23 A 7 IEEE STD 488 GPIB System Concepts 494P Programmers DEVICE DEPENDENT MESSAGES The IEEE standard does not specify the coding of device dependent messages messages that control the internal operating functions of a device After addressing a talker and the required number of listeners via interface control messages the controller unasserts the ATN line false on the bus When ATN becomes false high any commonly understood 8 bit binary code may be used to represent a device dependent message The standard recommends
55. 490 07 IS 3807 6S 073S X001 0 paed 8S paje uoyesedo Auzeo oya Buuni Zs 1043 jeUsOPU 1X3 0 p ueyo 39u931331 Aouenbely 9S 1NI 0 pebueyo eoueseje2 kou nb i s9 suue jBu44U yo pawn 4y YONN vS sayng ejdsip jo esn ajdynw es uo paum yui WONN ZS 0 0 payNnejep NYdS ts XVW 0 paHNejep NVdS 0S eBueud HXWXa pesneo eBueyo OFWI 6p sBuwem uORNDeXy puBUWOS YISHd ym Anoaap NO AIO pauan 3q JOUUBD MISHA 8p ebues jo NO WWOSYA 40 SHOLSG Twosy SHOLS 4t afuel jo NO ASWNN 9p paynoaxe you panou 65u eynoexg dnoip 139 Sv np ueds siy ul pamoye you spuy jeubig Oy npjueds siu ul pemoye you AWINACL 6 aGuesjomOAWIL ZE abue jo MO HOTdSALYA 9E abuel jo MO NIT dSALBYA SE ue jo NO AIH PE aue jo MO LIVNI JO HMdXYW _ebues jo no MASIY ZE auei jo INO NYdS LE aue jo o sqUuD oe afuel jo MO ONHOHA 6g aBues jo yno GNOOSS 40 LSHId SNNL Odus 8z pow jevo ul puewwoo apnoaxe 0 dwany 4g 3S0 ndino Buywyeusas moyyearo soyNganding JZ s4013 UONNIEXy mojpano yng mdu pZ peziuBooe you yuawnGie Ley ZZ Jepeey sju 10 pamoye jou quownBue jepods iZ paziuBooe you edAy uoun jeoeds oZ yuawnse siy 40 pemoye Jou yu pL Jepeay siy 10 pomoyje you puounbe Heug t yapeRay siu 40 pamojje OU quewnbse Bus ZL yepeey siu 40 pomoje 10u puawnue UNN LL yepeey siu 10 pomoje you pueunbue 10081840 OL Bujssiu syuawngue payoedxe jou yun aBesseui jo pug pezjuBooa jou J PL H pezjubooes you MND y
56. 494P using 4050 Series BASIC for examples We hope this information will speed your progress in putting the 494P to work solving your measurement problems NOTE In the examples throughout this section the 494P pri mary address is assumed to be 1 See Section 1 for how to set the GPIB ADDRESS switches Some of the lines of input in exampies of controller programs in this section extend beyond the column width limitations Where this occurs the overrun in formation is indented on the immediately following line important whenever a line is broken it is always where a natural space occurs So be sure to add a space when inputting the program DATA ACQUISITION When the 494P is acquiring spectrum data under pro gram control there are two programs running not just one One program is running in the controller and a second in the 494P The key to success is synchronizing the execution of the two programs In addition the execution of the two programs must be synchronized with the event that accomplishes data acqui sition in this case the sweep Synchronizing Controller and 494P Program execution in the controller can be synchronized with 494P execution of messages it receives over the GPIB This is all done within the 494P by the way it buffers and executes messages When the 494P receives a message it waits until the end of the message to begin execution While busy executing the message the 494P does not accept
57. 494P begins transmitting if there is no listener the message NO LIS TENER is flashed to the operator and the 494P returns to local control 7 To move to the next 4924 file press Forward To move to the previous file press Reverse To move to the beginning of the same file press Reverse then Forward Restoring Control Settings and the Display From Tape With the LISTEN ONLY switch set the 494P buffers and executes device dependent messages except for interrupt control commands EOS and RQS Since the remote local state diagram in the IEEE 488 standard does not cover the listen only mode this mode is implemented in the 494P so it goes to the remote state after buffering a message This makes the listen only mode consistent with the nonlisten only mode The nonlisten only mode requires that the 494P be under remote control to execute commands that change front panel settings or waveform data in digital storage To restore control settings and a previously recorded dis play find the file on the tape using Forward or Reverse on the 4924 and press Talk The 494P goes to remote to exe cute the message and then returns to local control The listen only mode can be used for a comparison test Settings and a waveform previously recorded with SAVEA on can be played back to the analyzer The analyzer auto matically sets up to make the same measurement turning on SAVEA and saves the comparison waveform in A mem ory If B SAVEA is
58. ANUAL PEAK control is ac tive AUTO PEAK is turned off so the operator can manually peak the analyzer s response from the front panel The omission of the argument is equivalent to AUTO PEAK Power up value KNOB AUTO PEAK off MANUAL PEAK on 1 PEAK peaking query CRD 6415 153 Response to PEAK query a D KNOB 4415 154 a REV MAR 1985 Front Panel Control 494P Programmers PEAK MINATT MINATT minimum RF attenuation command Ganarr 4415 155 NUM The gain distribution set by the microcomputer is limited RF attenuation may not be reduced below the attenuator step in the number argument If NUM is not an even decade from 0 to 60 the next higher step 0 10 20 60 is selected INC or DEC The minimum RF attenuation is changed to the next higher or lower step if any Power up value MIN RF ATTEN dB control setting Interaction The range of RF attenuation is limited in response to the REFLVL command which limits the range of the REFLVL command The previous limit set by either MINATT or MAXPWR is cancelled MINATT minimum RF attenuation query 4415 158 Response to MINATT query Omn 4415 157 4 21 Front Panel Controi 494P Programmers MAXPWR PLSTR MAXPWR maximum input power command Gtor WE JAn as 4415 158 NUM This is an input to a 494P microcomputer algo rithm that protects the RF INPUT from
59. BLE CONTROLS We can keep this simple because the 494P lets you make complex spectrum measurements semi automatically Many measurements can be made with just three front panel settings FREQ SPAN DIV and REF LEVEL The FREQ setting changes the center frequency position of the spectrum window you are viewing tuning the ana lyzer to change the frequency at the center of the crt The SPAN DIV setting changes the size width of the window setting the frequency calibration of the crt horizon tal axis The REF LEVEL setting raises or lowers the window which sets the amplitude calibration of the top graticule line on the crt Here s how to program the 494P to measure the CAL OUT signal using the front pane pushbuttons for these three settings 1 The CAL OUT signal can be centered by pressing the lt SHIFT gt FREQ 1 0 0 MHZ pushbuttons 2 Span down to look more closely at the signal by pressing the lt SHIFT gt SPAN DIV 1 MHZ pushbuttons The 494P automatically picks resolution bandwidth and time division to fit the new span division unless Auto Reso lution and Time Auto are cancelled For most purposes leave the TIME DIV control set to AUTO so that Time Auto is in effect in either local or remote control 3 Set the signal to the reference level by pressing the lt SHIFT gt REF LEVEL 2 0 dBM pushbuttons The 494P automatically selects the appropriate input attenuation and IF gain for a reference level at the p
60. ENT query EDON NR1 represents an event code that is defined at the end of this section in the ERROR and EVENT Codes Table 7 4 The event is cleared when the event code is reported 4415 76 ALLEV all events query GO 7 8 Response to ALLEV query Ra OOST 4415 78 The NRts represent the event codes that are defined in the EVENT and ERROR Codes at the end of this section Table 7 4 The events are cleared when their event codes have been reported NUMEV number of events command Numey JSP e NAT je 4415 79 NR1 This specifies that a fixed number of event codes is to be returned in ALLEV If fewer events are pending when ALLEV is executed the response is filled with zeros to provide the specified number The zero value sets the 494P to return a variable number of event codes Power up value 0 NUMEV number of events query 4415 80 Response to NUMEV query 4415 81 EVQTY event quantity query 4415 82 Response to EVQTY query 4415 83 NR1 specifies the number of events that will be returned in the next ALLEV If the NUMEV setting is 0 and EVQTY is not executed ALLEV returns an unspecified number of events TEST internal test query Cs O 4415 84 This command checks the system ROMs and RAM Response to TEST query CDBG O H O RAM NRI e 4415 85 The TEST query response consists of two decimal num bers that indicate if a ROM or
61. HE 4924 Data Logging To operate with the 494P the Mode Control switches on the 4924 rear pane must be set as a pair in any combination except SW1 OFF and SW2 ON Set SW1 to ON and SW2 to OFF same as for operation with the 4051 or set both switches to the same position both SW1 and SW2 ON or OFF With the 494P TALK ONLY switch set down you can write spectrum data onto a tape in the 4924 using the con trols shown in Figure 1 5 1 Insert a marked tape into the 4924 The tape must be previously marked for the size and number of files you ex pect to record Use the MARK command to mark the tape in a 4050 series controller MARK n 4500 TEETAN PRESS TO TRANSMIT TO 494P ADVANCE TAPE TO START OF NEXT FILE REWIND TO START OF PRECEDING FILE Figure 1 5 4924 controls used for data transfers This command marks n a number you choose files to be big enough to store both a waveform and its control settings on each file 2 Connect the 4924 and 494P with a GPIB cable after both are powered up 3 Set the 4924 On Line switch out off line 4 Rewind the tape 5 Press the 4924 Forward button to advance the tape to the beginning of file 1 To reach a file further into the tape press Forward again as many times as desired 6 To save the current 494P control settings and wave form in digital storage press Listen on the 4924 and RESET TO LOCAL on the 494P Press the RESET TO LOCAL bu
62. Hz 10 MHz div 800 ms 50 kHz 32 5 ms 100 MHz step 10 MHz div 150 ms 5 kHz 40 5 ms 0 1 8 GHz 1 MHz div 14s 500 Hz 156 ms ap Rare Step 1 Mh2 aiy are REFLVL RLMODE MINATT Add 100 ms TUNE MAXPWR if RF attenuator is 100 kHz step 100 kHz div 80 ms switched 100 Hz step 100 kHz div 60 ms 100 kHz step 100 Hz div 145 SAEAOTO 5s 100 Hz step 100 Hz div 14s PEAK AUTO 10 6 s 10 ms div COUNT DSTORE display 145 ms 1 Hz resolution 2 6 s P 1 kHz resolution T255 DRECAL display eoms CNTCF STORE settings 14 ms 1 Hz resolution 2 85 RECALL settings 425 ms 1 kHz resolution 1 75s CURVE 100 ms DEGAUSS cf 100 MHz 5 5 MHz div 700 ms GURVE poms 50 kHz div 820 ms POINT X argument only 56 ms 500 Hz div 980 ms FIBIG 760 ms EXMXR and FRQRNG if input Add 150 ms per LFTNXT RGTNXT 100 ms signal transfer switch or switch separation in div preselector LPF switch is changed p SPAN to phase lock span 220 ms RMAXPEMIN eos boundary 10 kHz div to 1 MHz div 7 SET command execution time 520 ms to 6 8 s INIT 500 ms TEST 6s REV FEB 1984 gt Because of the way the 494P handies output the micro computer is free after it loads an output buffer The addi tional time for the transfer is related to the listener for cases where the 494P is faster For instance with 4051 and 4050 Series controllers the following transfer times have been observed Tabie 8 2 REV FEB 1984 Helps and H
63. IC statements do the same job as the 4050 Series waveform INPUT subroutine 5000 REMARK TEK SPS BASIC WAVEFORM INPUT SUBROUTINE 5010 PUT CURVE INTO N LZ 5020 RASCII W FROM N TZ 5030 RETURN Array W must be dimensioned using INT 1000 RASCII Operates as noted for the 4050 Series INPUT statement i e it ignores non numeric characters and proceeds to fill the array when it receives numbers 9826A Controller Here s a self contained program for input of a 494P waveform So the program can operate with minimum mem ory it inputs a half resolution waveform 500 points O wti 0 7 l dim WI500 1 2 wrt 2 wfmpre wfid A curve 3 rdb z rl 4 if vrl 44 rdi 4ri rdi 4rl jmp 0 53 wait 1 6 11 7 for I 1 to 500 8 red z A 9 AWII 10 next I Line 2 The wfmpre command selects memory A for transfer Lines 3 and 4 Read the ASCII bytes in the curve re sponse until the comma that precedes the first number is detected Lines 7 through 9 The loop inputs the waveform data Of course you must have assigned z to the 494P with a device statement as explained earlier in this section under Setting Programmable Controls GETTING SMARTER Signal analysis can be even easier Put the 494P micro computer to work to find and measure signals with its inter nal waveform processing capabilities The full set of waveform processing commands is described in Section 6 and more instructions for t
64. LOG 10 dB REFLVL 30 dBm CAL OFF FINE OFF RLMODE MDIST PEAK KNOB AUTO PEAK off MINATT Knob position PLSTR OFF TRIG FRERUN SIGSWP OFF TIME Knob position AVIEW ON BVIEW ON SAVEA OFF BMINA OFF MXHLD OFF CRSOR KNOB REDOUT ON GRAT OFF PT OFF 500 YOFF 225 CLIP OFF TEXT SHORT EOS OFF RQS ON NUMEV 0 System Commands and Queries 494P Programmers INIT ID Interaction IEEE 488 interface functions are not af fected and the instrument remains under remote control RQS is set to OFF if either the LISTEN ONLY or TALK ONLY switch is set There is no INIT query ID identify query 4415 63 Response to ID query VINR2 Tektronix Interface Standard for GPIB Codes Formats Conventions and Features version number FV NR2 Instrument firmware version number FPV NR2 Front panel processor firmware version number 7 3 System Commands and Queries 494P Programmers WAIT REPEAT MESSAGE EXECUTION The foliowing two commands WAIT and REPEAT affect how the 494P microcomputer executes message units im bedded within other messages WAIT wait for end of sweep command a 4415 64 The 494P microcomputer delays execution of commands in its input buffer that follow the WAIT command While the microcomputer waits it sets its GPIB status byte to busy and does not input device dependent messages The wait condition is terminated in either of two ways 1 WAIT is terminated if an end of sweep is
65. MAXPWR maximum input GET Group Execute Trigger 3 5 POWER ne AENA ses 4 22 EVENT ERR Codes 3 6 PLSTR pulse stretcher 4 22 Preserving Frequencies 3 6 VIDFLT video filter 4 23 MINATT Command 3 6 Sweep Control 0 0 eee 4 24 Reference Level 3 6 TRIG triggering 4 25 RDOUT Command 3 6 SIGSWP single sweep 4 26 INIT Command 0005 3 6 TIME time div 4 27 Digital Storage Control 4 28 FRONT PANEL CONTROL AVIEW and BVIEW A and B waveform display 4 29 Introduction a g c4 aiaann da wenger 4 4 1 SAVEA save A waveform 4 29 PrOQUENCY sched E EE E ole 4 3 BMINA B A waveform display 4 30 FREQ center frequency 4 4 DSTORE store display 4 30 TUNE incremental frequency DRECAL recall display 4 30 change ee eee eee 4 4 MXHLD max hold 4 31 FIRST ist LO frequency 4 5 CRSOR peak average cursor 4 31 SECOND 2nd LO frequency 4 5 Display Control 4 32 DISCOR disable tuning Display control command 4 33 COMECHIONS oo ee Rhee ees 4 6 General Purpose 4 34 FROQRNG frequency range 4 6 HELP help 2 4 34 COUNT counter 4 7 STORE store settings 4 35 CRES counter resolution 47 RECALL recall settings 4 35 CNTCF count to
66. NTENTS cont J Page Page Section 3 DEVICE DEPENDENT MESSAGE Section4 FRONT PANEL CONTROL cont STRUCTURE AND EXECUTION cont Num a una Hae eae 3 3 DEGAUS degauss tuning coils 4 8 WINS 3 0 5 xed axes es fa hes 3 3 EXMXR external mixer input 4 9 Character Argument 3 4 Frequency Span and Resolution 4 10 Link Argument 3 4 SPAN frequency span division 4 11 String Argument 3 4 ZEROSP zero span mode 4 11 Query Format ossos kiniss 3 4 MXSPN max span mode 4 12 Binary BlOCK so curses nears tes 3 4 RESBW resolution bandwidth 4 12 Enid DEK its 4 5 4 spate waar ate 3 4 ARES automatic resolution 494P Output Messages 3 4 bandwidth 0 4 13 Output Message Format 3 4 IDENT identify 4 14 Output Message Execution 3 4 Vertical Display and Reference Level 4 15 494P 492P Compatibility 3 5 VRTDSP vertical display 4 16 GPIB oct OOE soc arcing OF 3 5 REFLVL reference level 4 17 DEGAUS Command 3 5 CAL Call x js ave grea nis ines aye otssene 4 18 IDENT Command 3 5 FINE fine reference level steps 4 19 PEAK Command 3 5 RLMODE reference level mode 4 20 Readout Maximum 3 5 PEAK peaking 4 4 20 Service Requests MINATT minimum RF Affect of Busy on Device attenuation 0 4 21 Dependent Messages 3 5
67. P7470A plotter The plotter must be in the listen only mode A bus controller is not required ADDRESSED This button lights when the analyzer is addressed to lis ten or talk GPIB Function Readout A single character appears in the lower crt readout when the 494P is talking T listening L or requesting service S see Figure 1 2 Two characters will appear in this loca tion if the 494P is talking or listening and also requesting service 300EM g FREQU 7 ae HZD V et CHE HAK er HH HHH l doad Li an ews i salas 1B ing 8 a ie ans RANCE OSCILLATOR _ BANDWIDTH T TALKER L LISTENER sS SERVICE REQUEST Figure 1 2 Status of active GPIB functions l GPIB ADDRESS LF or EO TALK ONLY LISTEN ONLY 1 Figure 1 3 Rear panel GPIB ADDRESS switches The LF OR EOI switch message terminator and the TALK ONLY and LIS TEN ONLY switches are part of the same switch bank _ TEE i Setting the GPIB ADDRESS Switches The rear panel GPIB ADDRESS switches shown in Fig ure 1 3 set the value of the 494P GPIB addresses refer to Table 1 1 The instrument s primary address 0 through 31 is the value of the lower five bits which are switches 4 through 8 The listen and talk addresses are set by the two left most switches The internal microcomputer reads these switches at power up and again each time the RESET TO LOCAL
68. PRE and CURVE queries The display preamble DPRE contains the numeric data necessary to reproduce the display The display units necessary to make a hard copy of a display DCOPY can be transmitted to another unit WFMPRE waveform preamble command 4415 35 The WFID path of the waveform preamble command al lows the choice of either the A or B waveform or both FULL Following the ENCDG path the waveform preamble command allows selection of either ASCII coded decimal or binary waveform data The contents of digital storage determine if a half resolution or full resolution waveform is obtained or two dif ferent waveforms This is because of the way digital storage is handled in the 494P The B waveform is updated with each sweep the A waveform is updated only if SAVEA is OFF The values stored for each waveform are alternate points on the current display B0 AO B1 A1 B2 A2 With SAVEA OFF each waveform is a half resolution replica of data from the last sweep A data points offset by 1 from corresponding B data points Full resolution FULL transfers merge the two waveforms for 1000 data points 100 points div and haif resolution transfers A or B sepa rate the waveforms for 500 data points 50 points div If the waveforms are separated signals resolved to a single point with very narrow resolution bandwidths compared to span appear in either A memory or B memory but not both With SAVEA ON onl
69. RAM IC was found to be defective These numbers must be translated to their binary equivalents to determine the ROM and RAM locations re spectively If all ROM and RAM are good the TEST query response will be ROM 0 RAM 0 After the binary numbers are determined put them into the conversion charts in Fig ure 7 1 to identify the IC number Then use Table 7 3 to find the correct circuit number and circuit board The following example shows how to use the conversion charts and Table 7 3 If any ROM or RAM ICs are indicated to be bad refer this information to qualified service personnel Example Enter 100 PRINT A TEST 100 INPUT A R 120 PRINT R If the TEST query response is TEST ROM 4112 RAM 18 then ROM 1 The binary equivalent of the ROM number 4112 is 01000000010000 2 Insert this binary number in part A of Figure 7 1 right justified Blocks 6 and 2 will be 0 1 This indi cates that both ROM 6 and ROM 2 are bad all other ROMs are good 3 Table 7 3 shows that ROM 6 is U2018 and that ROM 2 is U1018 both located on the GPIB board System Commands and Queries 494P Programmers TEST RAM 1 The binary equivalent of the RAM number 18 is 10010 2 Insert this binary number in part B of Figure 7 1 right justified Blocks 5 and 2 each contain a 1 which indicates that both RAMs 5 and 2 are bad all other RAMs are good 3 Table 7 3 shows that RAM 5 is U2044 and RAM 2 is U1027 both located on
70. REPEAT the nested REPEAT will only be exe cuted on the first pass through the commands that precede the second REPEAT For example RGTNXT FREQ REPEAT 10 FREQ 15 GHZ REPEAT 1 This causes the 494P to output 12 frequency values after it executes the message because it only executes the fre quency query once on its second pass through the entire message Interaction A REPEAT loop can only be aborted by DCL Pressing RESET TO LOCAL does not abort the loop it only causes execution errors to be reported if the loop contains front panel commands If RESET TO LOCAL is pressed while a message that includes REPEAT is being executed the message execution will be limited to 256 times Since most commands are ignored after the RESET TO LOCAL button is pressed the REPEAT loop compietes quickly System Commands and Queries 494P Programmers EOS RQS STATUS AND ERROR REPORTING Two commands EOS and RQS control 494P service requests The status byte reports instrument status in a for mat that implements both IEEE 488 and the Tektronix Inter face Standard for GPIB Codes Formats Conventions and Features GET is enabled to trigger a new sweep DT A query EVENT returns detailed information about events reported in the fast serial poll status byte Two queries and one command ALLEV NUMEV and EVQTY specify the identity and quantity of events reported Two queries ERCNT and ERR are included for 492P compatibil
71. STARTED cont List Of Tables ste elec dado eh nde ereer vi List of Ilustrations 20 eee vi Querying Programmable Controls 2 3 Safety Summary 0 0000 c cea eee eue viji 4050 Series Controller 2 4 CP1100 and CP4100 Series Section 1 INTRODUCTION TO GPIB OPERATION Controllers cceeeeeee 2 4 Introduction aean a E aA 1 1 9826A Controller 2 4 GPIB Controls and Indicators 1 1 Summation oaaae 2 4 RESET TO LOCAL REMOTE 1 2 Exercise Routines 2 5 lt SHIFT gt PLOT 4 2 Listen Talk 00 2 5 ADDRESSED 1 2 4050 Series Controller 2 5 GPIB Function Readout 1 2 CP1100 and CP4100 Series Setting the GPIB ADDRESS Controllers ie 25 Switches 0 cece eee 1 3 9826A Controller 25 Setting the LF OR EOI Switch 1 3 Acquiring Instrument Settings With TALK ONLY LISTEN ONLY BE Dnt eee talon es avis rei 26 Switches o Loau 1 4 4050 Series Controller 2 6 Talk Only Listen Only Operation 1 4 Resetting the 494P and Interface 494P Operation With the 4924 1 5 Messages m rora an aeiaai al Data Logging 0 00 1 5 4050 Series Controller 2 7 Restoring Contro Settings and CP1100 and CP4100 Series the Display From Tape 1 6 Controllers 6 sees eee 2 7 Putting a Counter on the Tape 1 6 9826A Controller 2 7 IEEE 488 Functions 1 7 Acquiring a Waveform
72. T PARAMETERS The queries SET and ID and command INIT in this group return settings and identification parameters and ini tialize settings SET instrument settings query ow SET ad 4415 60 Response to SET query The Instrument returns a string of commands that can be learned for later transfer to the 494P when the same setup is desired The response includes only those functions necessary for such a setup To assure no interaction with the 4 A mode that might alter the setup FINE OFF precedes the string to turn FINE off before the setup begins of ON Y N PRORNG SP NR1 G EXMXA SP bs AEJ SERA MNoIse eat ove emo 6 cm OFF MDIST a nat Fy E re ee a _ oN gt R3 G FRE Je SP el nas o O lt SPAN Pa ihn cl ae E eer Sjoe H NR3 j Some came ODO OFF eCauto Lows O pr cae en POOL 4415 61 INIT initialize settings command eas 4416 62 INIT resets the instrument the same as if the power was turned off then turned back on The instrument functions are reset as shown in Table 7 2 Table 7 2 INSTRUMENT FUNCTIONS Mnemonic INIT Value FREQ 0 FIRST 2 072E 9 SECOND 2 182E 9 DISCOR OFF COUNT OFF CRES 1 Hz DELFR OFF ZEROSP OFF RESBW 1 MHZ ARES ON MXSPN OFF PHSLK OFF VIDFLT OFF VRTDSP
73. TERK m OGRAMMER SS iy Part No 070 4415 00 w MANUAL ee tte ge So Product Group 26 ee 494P SPECTRUM ANALYZER 494P Programmers PREFACE This manual is one of a set for the TEKTRONIX 494P and non programmable 494 Spectrum Analyzers The man uals that are available at this time in addition to this 494P Programmers are the 494 494P Operators 494 494P Oper ators Handbook a smali manual that fits in the instrument front cover and 494 494P Service Volumes 1 and 2 Refer to the 494 494P Operators manual for a full de scription of instrument functions and front panel controls The Operators manual also contains the full specification of instrument performance This manual describes the programmable functions of the 494P and how to use them for remote operation Sections 1 and 2 help you get started using the 494P on the IEEE Std 488 General Purpose Interface Bus GPIB Programming examples are included here as well as throughout the manual Some examples are given for a vari ety of GPIB controllers but most are in BASIC as imple mented on TEKTRONIX 4050 Series controllers Comments are included to help you translate if you are using another controller Sections 3 through 7 are a reference to the language used to set and read 494P functions and transfer spectrum data acquired by the 494P Section 3 defines device dependent message format and execution Sections 4 through 7 cover the commands and queries by fu
74. UN f FREQUENCY RANGE FRQRNG 3 VJ a Digital St COUNTER COUNT 4 babendil COUNT RESOLN CRES 5 COUNT gt CF CNTCF 6 VIEW A AVIEW 28 AF DELFR 7 VIEW B BVIEW 29 Degauss DEGAUS SAVE A SAVEA 30 EXT MIXER _LeXMxR 8 B SAVE A BMINA 31 STORE DISP DSTORE 32 Frequency Span and Resolution RECALL DRECAL 33 MAX HOLD MXHLD 34 FREQUENCY SPAN DIV PEAK AVERAGE CRSOR 35 amp SPAN DIV ENTRY SPAN 9 Display Control ZERO SPAN ZEROSP 10 MAX SPAN MXSPN 11 RESOLUTION BANDWIDTH RESBW 12 READOUT REDOUT 36 AUTO RESOLN ARES 13 GRAT ILLUM GRAT 37 IDENT IDENT 14 BASELINE CLIP CLIP 38 Vertical Display and Reference Level Generai Purpose 10dB DIV HELP HELP 39 2dB DIV VRTDSP 15 STORE STORE 40 LIN amp dB DIV ENTRY RECALL SETTINGS RECALL 44 REFERENCE LEVEL PLOT PLOT 42 amp REF LEVEL ENTRY REFLVL 16 Plotter Type Selected PTYPE CAL CAL 7 Plot B A K Formula POFSET FINE FINE 18 MIN NOISE MIN DISTORTION RLMODE 19 Command related to front panel contro functions not actually MANUAL PEAK AUTO PEAK PEAK 20 a 494P labeled front panel control MIN RF ATTEN dB MINATT 21 bReters to Figure 4 1 MAXPWR 22 PULSE STRETCHER PLSTR 23 WIDE VIDEO FILTER NARROW VIDEO FILTER VIDFLT 24 4 2 REV FEB 1984 i The following controls are operated only from the front panel no remote control INTENSITY MANUAL SCAN POSITION AMPL and LOG CAL POWER PEAK AVERAGE cursor other than fully counter clockwise or clockwise positions Front Pa
75. Up to 15 devices can be connected To maintain bus electrical characteristics no more than one 2 meter cable should be connected for each device one for the controller one for the 494P etc and at least two thirds of the devices connected must be powered up Appendix A details the IEEE STD 488 GPIB System Concepts z 15 V MAX OUTPUT IER CORD PROTECTIVE GROUNDING EARTH GROUND DO NOT REMOVE LIFIED PERSONNEL JEEE STD 488 PORT Figure 1 6 The rear panel IEEE STD 488 PORT GPIB 1 8 if an internal switch is changed the 494P asserts SRQ on power up This requires immediate action by some con trollers such as Tektronix 4050 Series so is not recom mended for these controllers Other internal switches select self test modes at power up changing these switches pre vents the 494P from operating normally Because changing these switches requires that the cover be removed refer this task to qualified service personnel A turn on procedure is provided in both the 494 494P Operators Manual and the 494 494P Operators Handbook Refer to those books for instructions on how to begin op erating the instrument The power up condition of all programmable functions is restored by the INIT command Refer to Section 7 for more on this command and a list of the power up parameters 4415 07 Figure 1 7 The 494P can be connected to a GPIB system in either a star A or a linear B configu
76. action DRECAL turns SAVEA ON If SIGSWP is off the current instrument sweep readout is displayed J MXHLD max hold command 4415 187 ON Digital storage holds the maximum value obtained for each point in both the A and B waveforms a point is updated only if the new value is greater than the current value The A waveform is not affected if SAVEA is on OFF B waveform is continuously updated A wave form is updated only if SAVEA is OFF NUM 1 equals ON numbers 0 5 are rounded to 1 Number 0 equals OFF numbers less than 0 5 are rounded to 0 Power up value Off MXHLD max hold query O 4415 188 Response to MXHLD query woe E 4445 489 Front Panel Control 494P Programmers MXHLD CRSOR CRSOR peak average cursor command 4435 190 KNOB The PEAK AVERAGE knob is under focal con trol The operator can set the cursor level which is shown by a line across the crt Above the line peak values are stored as each point is updated below the line averaged values are stored PEAK The peak value digitized at each point is used to update digital storage regardiess of the cursor position last set by KNOB This is the same as setting the cursor to its lowest minimum position AVG Average values are used to update the wave forms regardless of the cursor position last set by KNOB PEAK AVG is the same as if the cursor is set to its highest
77. addressed as a talker The ana lyzer operates in a simple system in a listen only mode if the LISTEN ONLY switch is set to 1 Service Request SR1 The 494P employs the complete service request func tion asserts SRQ for the conditions indicated under Status Byte in Section 7 and reports the corresponding status when polled Remote Local RL1 The 494P employs the complete remote iocal function The front panel RESET TO LOCAL button returns the in strument from remote to locat control unless the LLO locat lockout message was previously received The GTL go to local message also returns the instrument from remote to local control Refer to the discussion under Status Byte in Section 7 for the affect of busy status on remote local transitions The current value of all programmable functions is main tained when switching from local to remote control Only the value of TIME MINATT and CRSOR may change to match the front panel control settings when switching from remote to local control since they don t conflict with local control In either case all front panel indicators show the current value of the functions The analyzer must be under remote control to begin exe cuting device dependent messages that change the state of local controls or to load data into digital storage Once be gun execution continues even if REN goes false The ana lyzer changes settings for which there is no local control and outputs data while und
78. adout Then when MXSPN is turned off the previous FRE QUENCY SPAN DIV setting is restored 4 12 RESBW resolution bandwidth command SP MHz 4415 128 NUM The nearest available resolution bandwidth is selected numbers between bandwidths that can be se lected from the front panel are rounded by a geometric algo rithm Positive numbers above or below the range of bandwidth steps are rounded to the nearest step an error message appears on the screen if the argument is beyond the normal range Zero and negative numbers cause an error The geometric algorithm rounds the value to a single significant digit If the digit is above the breakpoint the next higher bandwidth step is selected If the digit is equal to or Jess than the breakpoint the next lower step is selected For values above 100 the breakpoint is 3 for values below 100 the breakpoint is 5 refer to Table 4 2 Table 4 2 RESOLUTION BANDWIDTH SELECTION Value Selects 5 48 Hz 54 7 Hz 30 Hz 54 8 Hz 316 Hz 100 Hz 317 Hz 3 16 kHz 1 kHz 3 17 kHz 31 6 kHz 10 kHz 31 7 kHz 316 kHz 100 kHz 317 kHz 3 16 MHz 1 MHz a Values outside the ranges listed cause an out of range error message to appear on the screen Sy 4 AUTO Auto resolution is selected equivalent to ARES ON INC The next larger step is selected if possible DEC The next smaller step is selected if possible Power up valu
79. ages on the 4O4P Ort oii aie ene lad eqs 8 1 IEEE Std 488 GPIB connector A 2 A typical GPIB system 1 A 4 ASCII amp GPIB Code Chart A 7 An example of data byte traffic on the GPIB A 9 A typical handshake timing sequence idealized siete ics i Ae eaae S A 9 494P Front panel controls 494P Programmers vij 494P Programmers SAFETY SUMMARY The safety information in this summary is for both op erating and servicing personnel Specific warnings and cau tions will be found throughout the manual where they apply but may not appear in this summary CONFORMANCE TO INDUSTRY STANDARDS The 494P complies with the following Industry Safety Standards and Regulatory Requirements Safety CSA Electrical Bulletin FM Electrical Utilization Standard Class 3820 ANSI C395 Safety Requirements for Electrical and Electronic Measuring and Controlling instrumentation IEC 348 2nd Edition Safety Requirements for Electronic Measuring Apparatus Regulatory Requirements VDE 0871 Class B Regulations for RFI Suppression of High Frequency Apparatus and Installations TERMS In This Manual CAUTION statements identify conditions or practices that could result in damage to the equipment or other property WARNING statements identify conditions or practices that could result in personal injury or loss of life viii As Marked on Equipment CAUTION indicates a personal injury hazard not i
80. allows you to enable both talk only and listen only operation if 494P power is on press RESET TO LOCAL or lt SHIFT gt PLOT to cause a change in these switches to take effect Both the TALK ONLY and LISTEN ONLY switches must be off down when the 494P is used with any controller Set the LF OR EO switch to EOI down for use with Tektronix equipment The switches marked 1 2 4 8 and 16 may be set to any combination except all ones decimal 31 which logically disconnects the 494P from the bus SWITCH DOWN OPEN EO ME Set for use with Tektronix controllers OUTPUT Talk Only Listen Only Operation The 494P can be operated as a talker only or a listener only on the GPIB under local control This requires only the 494P and a talker or listener Such a system uses the TEKTRONIX 4924 Digital Cartridge Tape Drive with the 494P This system can be used to save spectrum measure ments for later display on the 494P or for analysis by a controller This system will also save and restore analyzer control settings Follow the Data Logging instructions under 494P Operation with the 4924 SWITCH UP ge TY 3 ro El tol tol fo ol o OPEN EO E Set for use with controllers not manufactured by Tektronix OUTPUT LF amp EOI 4415 04 Figure 1 4 Etfect of message terminator switch for input and output 1 4 i Foeererees Introduction to GPIB Operation 494P Programmers 494P OPERATION WITH T
81. ameters Other options in These commands contro the sweep triggering and mode clude manual or external analog contro of the sweep TRIG and SIGSWP and sweep rate TIME Selection of Tektronix frEnticat VOEO DIGIAT DISMAY FILER STORAGE oO 8 FREQUENCY py RESOLUTION SPAN DW O BANOWIOTH REFERENCE Levet mayin AY ATTEN aD 2 260 60 see El en iol ate Famed tamos EXTERNAL cat Our output MIXER on naga ene Figure 4 5 Front panel Sweep Control commands 4 24 oy ni st TRIG triggering command 4415 167 FRERUN The analyzer sweep is allowed to run repeti tively A trigger is not required and is ignored so the ana lyzer generates a sweep immediately after the hold off period that follows the previous sweep This is a simple and common setup used to acquire a spectrum for manual operation INT The analyzer generates a sweep only when it is triggered by an input signal at its center frequency A signal amplitude of at least 2 divisions is required and must occur after the hold off period that follows the previous sweep This sweep mode is often used to examine time domain sig nals in zero span mode ZEROSP LINE The power line input is selected as the trigger signal useful in both the frequency and time domain modes for signais with components related to the power line frequency EXT
82. an 492P DEGAUS may be executed in spans 21 MHz div IDENT Command 494P The span must be lt 50 kHz for coaxial bands 0 21 GHz or lt 50 MHz for waveguide bands 492P The span must be at 500 kHz div PEAK Command 494P A PEAK value is stored for each band 492P The same value is used for all bands Readout Maximum 494P Readout strings can contain up to 40 characters 492P Readout strings can contain up to 32 characters REV FEB 1984 Service Requests 494P RQS is the master mask for service requests and both RQS and EOS must be on to cause end of sweep service requests 492P RQS masks error service requests and EOS masks end of sweep service requests Only EOS must be on for end of sweep service requests Affect of Busy on Device Dependent Messages 494P Interface messages are processed despite busy status If RTL interrupts a message the microcomputer ex ecutes the remainder of the message before restoring local control The response of the 494P to interface messages depends on the manner in which they are handled Some interface messages are handled by the GPIB interface while others require action by the microcomputer The latter gen erally involve the 494P GPIB address and are implemented in microcomputer firmware rather than on the interface The speed with which these commands can be handshaked de pends on how fast the microcomputer can service the re sulting
83. are rounded to 0 Power up value Off Interaction The EXT MIXER input is automatically se lected for the waveguide bands FRQRNG 6 and above and cannot be defeated by EXMXR OFF When active this input bypasses the input attenuator so it is up to the operator to prevent input overload EXMXR external mixer input query amo 4445 118 Response to EXMXR query 4415 117 49 Front Panel Control 494P Programmers FREQUENCY SPAN AND RESOLUTION Figure 4 3 The commands in this group control the frequency span the display Also true signals can be distinguished from SPAN the zero span mode ZEROSP the max span spurious frequency conversion products IDENT mode MXSPN and the resolution RESBW and ARES of Tektronix 494P ehi Sian RT fooonn SH tone CENTER FREQUENCY 7 o bs ae i 1 O 0 Do8 Data enay TERT EAT miaa DONAT DISPLAT FILTER STORAGE ZQ na Sno nesouurion FREQUENCY Treat SPANO O GANOWID TH REFERENCE LEVEL 9 man Eon Eea min vosotros B QO MON RF ATTEN aS 2 Figure 4 3 Front panel Frequency Span and Resolution commands 4 10 SPAN frequency span division command 4445 119 NUM The span division is selected The value of the argument is rounded to two significant digits Zero converts the analyzer to the time domain in zero span mode
84. ate the display For digital stor age to properly acquire spectrum data 2 ms div is the maximum usable sweep rate Front Panel Control 494P Programmers TIME TIME time div query 4415 174 Response to TIME query The SET response includes AUTO as a possible argu ment see SET under System Commands And Queries Section 7 NR3 bad EXT Came J6 4415 175 4 27 Front Panel Control 494P Programmers DIGITAL STORAGE CONTROL Figure 4 6 These commands control the 494P digital storage func recalling the display DRECAL and digitizer control tions of display AVIEW BVIEW updating SAVEA dis MXHLD CRSOR play and updating BMINA display storage DSTORE ai Tektronix A nance vo CENTER FREQUENCY ERICA Vaio UTAT Gisela PIER SOAGE other row pore oR ENC Y Gy RESOLUTION DATA EWEAY SPAN D BANDWIDTH REFERENCE Leys umar ATTEN S POWER O tannic haa 4415 13 Figure 4 6 Front panel Digital Storage Control commands 4 28 AVIEW and BVIEW A and B waveform display commands oe Con e ON The specified waveform is displayed on the crt The waveforms are independent and may be displayed to gether or separately however if SAVEA is off both wave forms are displayed if either AVIEW or BVIEW is on 4415 176 OFF The display of the specified waveform
85. b Buissaccig WIOJIALM AJUO OU Si ZLNJOd Pazed pu si anb ou ssaqun esgyuy IPLAY joueg UOL4 10 WAIS S O Beg Aejdsiq e jo Jeprey ey op yew uogsanb e Bulppe Aq Aanb g wod KELAA 40 3uyy Bre peuinbei eve gjuowauw L JO 184 99443 4811 L AjUD ginones6 jo do 0 jeus AAOU O jana 89U918491 eGUBYO feuBls yxeu 346u puid Aanb Buisseoosd wiojaaem u quiod gep Aejdsig WON A WAN X feuBls xau 4 puly WAN Pioysai i njea wnwuju pulg anjea winuwixew pul4 yeubls ysa66iq pul yeubls 49385 WNN Plousedyt WAN piosa Burssac01g WOpBAeA Auanb ou deams jo pua 10 YEM 388 PUsO U s6unjes Juewruysul senbay ysew OUS luUOUge HO 10 uo WNL dO NO uolnoaxe yeaday WNN S U949 JO JOQUUNN WN suas azyenuy juewinaysul Ayjuep UORRWUOJU JUBA sog unos Joug 10u00 OHS d ms jo puz 440 NO jqeu porebbyy aag 440 NO Syuan IY waysig g1quieesd WOJOARMA VADNI PUE AJM WUOJBARM ynopral uo saddn apow nopea ebueyD NO1 LYOHS WHYON 10 Aanb ou eBessaw ynopeas YO siajoeseyo Op 0 dN ynopees YO aMO7 aiqueaid Aedsiq Aeydsip Ado seug 4909 40 O n ejdsig ssabejul pue alAYD ost 82a Agidsig uonoung quownbiy SALON oBdOL AXNLOW tiN Od LLNIOd AXNLST NIN XVW ogidi SNIJO HYM tisa aS sou MESEIS AANNN AINE ai 4iN3AR igya e1NOYS 03 40 Aay audWdM WUsAVM coardn AXEL 4noau 2odko1 agda tada aano 4 P82H NYdS OX3Z AVIdSIO IYOILY3A
86. bers or a block of binary data To keep this simple let s discuss the ASCII here and cover the binary in the WFMPRE command in Section 5 The 494P powers up ready to transmit waveforms in ASCII the WFMPRE command in Section 5 explains how to change modes 4050 Series Controller Let s define another 4050 Series User Definable key for this job Incorporate the following input messages into the main program established under Acquiring Instrument Settings With SET earlier in this section When you press User Definable key 6 the following sub routine inputs a full 1000 point waveform with A and B memories merged a power up condition Array W in this program must be dimensioned to 1000 24 GOSUB 5000 25 RETURN 115 DIM W 1000 5000 REMARK 4050 SERIES WAVEFORM INPUT SUBROUTINE 5010 PRINT Z CURVE 5020 INPUT Z W 5030 RETURN Lines 24 and 25 Subroutines called when User Definable key 6 is pressed They jump to the subroutine that transfers the CURVE data Line 115 Dimensions array W to receive a full 1000 point waveform Line 5010 Requests waveform CURVE data 2 7 Getting Started 494P Programmers Line 5020 Ignores the ASCII characters that the 494P sends at the beginning of its CURVE response The INPUT statement then fills array W with the 1000 numbers trans mitted by the 494P See Section 8 for help in plotting the waveform CP1100 and CP4100 Series Controllers The following TEK SPS BAS
87. byte is the 494P response to a serial poll The ERR EVENT response is the 494P an swer to a device dependent query message The status byte provides information about instrument conditions by category normal abnormal busy command error execu tion error etc The ERR EVENT response details the cause of abnormal status i e what kind of error or warning prompted the 494P to assert SRQ and report abnormal sta tus Status bytes and EVENT responses are not stacked The code for the condition that caused the SRQ is not up dated although bit 5 reflects the present instrument state 1 for busy 0 for not busy The status byte is cleared by a serial poli of the instru ment Event codes are cleared when the event code is re ported Reading the status byte does not clear the error codes and vice versa DCL and SDC if addressed clear both the status byte and event codes FIRMWARE OPERATING NOTES Following are exceptions to normal instrument operation that relate to the different firmware versions The instrument displays its version number for approximately 3 seconds whenever instrument power is turned on or the RESET TO LOCAL REMOTE pushbutton is pressed Version 2 2 Plotting on a 4662 Option 31 Plotter The 4662 Option 31 plotter does not respond to the move command issued by the 494P immediately following the initial pen selection or a pen change command This results in the pen drawing from its home position rather
88. center PLOT plot data 4 35 frequency 20 005 4 7 PTYPE plotter type 4 36 DELFR delta frequency 4 8 POFSET set K 4 36 494P Programmers Section 5 Section 6 Section 7 TABLE OF CONTENTS cont Page DISPLAY DATA AND CRT READOUT VO MOGUCE oaia E 5 1 Waveform Transfers 5 2 WFMPRE waveform preamble 5 2 X Axis Scaling 2 5 3 Y Axis Scaling 5 3 CURVE display curve 5 4 WAVFRM waveform 5 5 DPRE disable preamble 5 6 X Axis Scaling ona SO Y Axis Scaling vee 5 6 DCOPY copy display 5 6 Crt Readout Transfers 7 RDOUT readout message 5 7 TEXT input text 00 5 7 UPRDO upper readout and LORDO lower readout 5 8 WAVEFORM PROCESSING Introduction s erae eee i 6 1 POINT display data point 6 1 FIBIG LFTNXT RGTNXT signal SEACH ose wets Seveseye meee Oana S 6 2 FMAX find maximum value 6 3 FMIN find minimum value 6 3 Display Data Point Commands Interaction 0 eee eee 6 3 CENSIG TOPSIG center or move SIQMAN 2 ds asters pate Sardine 6 4 SYSTEM COMMANDS AND QUERIES Introduction 6 e ee eee eee 7 1 Instrument Parameters 7 2 SET instrument settings 7 2 INIT initialize settings 7 3 ID identify 0 7 3 Message Execution
89. commands change analyzer settings automatically to center it exactly on the point Table 6 1 WAVEFORM PROCESSING COMMANDS AND QUERY Message Unit Function POINT Directs the microcomputer to a new display data point POINT Requests X and Y values of the display data point FIBIG Seeks the largest signal peak LFTNXT Seeks the signal peak to the left of the current point RGTNXT Seeks the signal peak to the right of the current point FMAX Finds the maximum Y value in digital storage FMIN Finds the minimum Y value in digital storage CENSIG TUNES the frequency to center the signal TOPSIG Moves the signal to the reference level The commands in this section update the display data point direct the microcomputer to a new point POINT find the largest or nearest signal FIBIG LFTNXT RGTNXT or search for the maximum or minimum value FMAX FMIN A query POINT returns the X and Y values of the display data point Commands that change the center frequency or the ref erence level to zero in on a signal use the X value CENSIG or the Y value TOPSIG This section covers how the waveform processing com mands and query work Two programs at the end of Section 2 show some of these commands in use Waveform pro cessing techniques are offered in Section 8 POINT display data point command OTA y ae a 4418 26 First NUM This is the X value of a display data point The horizontal scale is always the same a
90. cquired FIBIG LFTNXT RGTNXT signal search commands 4415 29 FIBIG find big This command seeks to acquire the largest signal peak with a point of greater value than NUM if a signal peak greater than NUM is not found the display data point is set to 500 0 LFTNXT left next This command searches to the left of the current point to acquire the peak of a signal whose value is greater than NUM If a signal peak greater than NUM is not found the display data point is set to 0 0 RGTNXT right next This command searches to the right of the current point to acquire the peak of a signal whose value is greater than NUM If a signal peak greater than NUM is not found the display data point is set to 1001 0 A pattern recognition routine and a threshold value are employed to recognize signals If the threshold value is omit ted from the command a default value of 0 is used Example FIBIG 100 LFTNXT RGT Interaction See Display Data Point Commands Interaction i i p FMAX find maximum value command SP _ Sm Onm 4435 30 This routine sets the display data point to the point in digital storage with the largest Y value If the largest Y value is located at more than one point the first left most point is acquired The optional arguments are two display X values The FMAX command will limit its search over this X range otherwise the full X
91. d arguments String Argument A string argument is used when a message is to be dis played on a printer plotter or display unit for human inter pretation as with the RDOUT command The characters are enclosed in quotes to delimit them as a string argument Query Format A query message unit requests either function or display data from the instrument The query message unit format is shown below saa a iraunen 4415 56 Binary Block Binary block is a sequence of binary numbers that is pre ceded by the ASCII code for percent and a two byte binary integer representing the number of binary numbers plus one the extra byte is the checksum and followed by the checksum The checksum is the 2 s complement of the modulo 256 sum of all preceding bytes except the first Thus the modulo 256 sum of all bytes except the first should equal zero to provide an error check of the binary block transfer wn E oem COUNT ARE CHECKSUM e BYTE BYTE 8 BIT ot BINARY NUMBER 4415 59 End Block End block binary is a sequence of binary numbers that is preceded by the ASCII code for at EOI must be as serted concurrently with the last data byte The end block can only be the last data type in a message 8 817 BINARY NUMBER 4415 58 494P OUTPUT MESSAGES When the 494P executes a query it buffers an output message unit that is a response to the query Output mes sage uni
92. d Device Clear DC SPDa Seria Poll Disable T TE SPEa Serial Poll Enable T TE SAQ Service Request via C TCTe Take Control Cc UNLa Unlisten L LE ES Remote Messages Sent ATN Attention Cc DAC Data Accepted AH DAV Data Valid SH DCLs Device Clear via C GET Group Execute Trigger via C ii GELE Go To Local via IFC Interface Clear C LLOa Local Lockout via C MSA My Secondary Address via C MTA My Talk Address via C PPCa Parallel Poll Configure via C PPDa Parallel Poli Disable via C a PPEa Parallel Poll Enable via C f PPU Parallel Poll Unconfigure via REN Remote Enable C om RFD Ready For Data AH SDCa Selected Device Clear via C i SPDa Serial Poli Disable via C as SPER Serial Poll Enable via C SRQ Service Request SR TCTa Take Control via C UNL Unlisten via C UNT Untalk via C Multi line messages A 5 IEEE STD 488 GPIB System Concepts 494P Programmers TALKERS LISTENERS AND CONTROLLERS A talker is an instrument that can send messages and data over the bus a listener is an instrument that can ac cept messages and data from the bus An instrument can be a talker only listener only or be both a talker and a listener Unless a device is in the talk only or listen only mode it can only communicate with other devices on the bus when it is enabled to do so by the controller in charge of the instru mentation system A controller is an instrument that determines by so
93. d and plotted Other MOVE and PRINT statement pairs could be added to label other points on the plot For instance to label the start frequency using the scal ing formula enter 830 MOVE 0 0 840 PRINT X1 X2 1X3 HZ 4 l Using PLOT The 494P can generate a piot of the display directly on the Tektronix 4662 or 4662 Opt 31 or a 4663 in the 4662 emulation mode or the Hewlett Packard HP7470A Plotter All selected waveform graticule and crt readout data can be plotted PLOT sent to the 494P causes it to output the plotter code when addressed as a talker Address the plot ter as a listener then monitor the EO line to allow the con troller to cause a plot to be generated without further intervention The following routine assumes the 494P is at address Z the plotter is at address P and that the plotter type has been selected with the PTYPE command 100 PRINT Z GRAT ON CLIP ON RDOUT ON PLOT 110 WBYTE 64 Z 32 P 120 ON EOI THEN 200 Helps and Hints 494P Programmers 200 WBY 63 35 210 RETURN Line 100 Illuminates the graticule turns the baseline clip and the crt readout on and readies the 494P to send a waveform to the plotter Line 110 Makes the 494P a talker and the plotter a listener Line 200 Untalks the 494P and unlistens the plotter MULTIPLE USE OF DISPLAY BUFFER FOR WAVEFORM PROCESSING AND 1 O An error message alerts you to possibly invalid data caused by multiple
94. d to 1 Number 0 equals OFF numbers less than 0 5 are rounded to 0 Power up value Off PLSTR pulse stretcher query TRO 4415 162 Response to PLSTR query we e 4415 163 i VIDFLT video filter command e Vibra 4415 164 OFF Both video filters are turned off WIDE A filter is turned on in the video amplifier after the detector to average noise in the display The wide filter reduces video bandwidth to about 1 30 of the selected reso lution bandwidth NARROW The effect of wide filter is magnified by a factor of 10 The narrow video filter reduces video band width to about 1 300 of the selected resolution bandwidth NUM 0 equals OFF numbers less than 0 5 are rounded to 0 Number 1 equals WIDE numbers gt 0 5 are rounded to 1 Number 2 equals NARROW numbers 1 5 are rounded to 2 Power up value Off Interaction it may be necessary to reduce sweep speed TIME because the analyzer s overall bandwidth is reduced by video filtering VIDFLT video filter query 4415 165 Response to VIDFLT query C TRO wee T 4415 166 Front Panel Control 494P Programmers VIDFLT 4 23 Front Panel Control 494P Programmers SWEEP CONTROL Figure 4 5 Three commands contro the 494P sweep which is used auto sweep directs the 494P to automatically match the both to sweep the frequency span and the crt display sweep to related analyzer par
95. e 1 MHz Interaction Any argument except AUTO cancels ARES ON Reducing resolution bandwidth may require a slower sweep speed TIME RESBW resolution bandwidth query 4415 129 Response to RESBW query 4415 430 The response to the SET query includes the AUTO argu ment see SET under System Commands And Queries Section 7 Front Panel Control 494P Programmers RESBW ARES ARES automatic resolution bandwidth command TEDN KOORO o CH Aj ON The microcomputer matches the current span with an appropriate resolution bandwidth that maintains cal ibrated performance for the current sweep speed If auto matic sweep speed is active the microcomputer selects an appropriate resolution bandwidth and changes the sweep speed to the fastest sweep that allows calibrated perfor mance ARES ON is cancelled by any RESBW command except RESBW AUTO 4415 134 OFF ARES ON is cancelled leaving the resolution bandwidth at the current value NUM 1 equals ON numbers 0 5 are rounded to 1 Number 0 equals OFF numbers less than 0 5 are rounded to 0 Power up value On Interaction ARES OFF also cancels RESBW AUTO ARES automatic bandwidth resolution query aie Oo a Os 4415 132 Response to ARES query Canes JGP 4415 133 ARES is not included in the response to the SET query 4 72 Front Panel Control 494P Programmers IDENT IDENT identify command 4415 134
96. e but indicators will still reflect the current state of ail front panel functions This button is not lighted when the analyzer is under local operator control While under local control the 494P does not execute GPIB messages that would conflict with front panel controls or change the waveforms in digital storage When the button is pressed local control is restored to the operator unless the controller prevents this with the focal lockout message Programmable functions do not change when switching from remote to local control except as necessary to match the settings of front panel controls for TIME DIV MIN RF ATTEN dB and PEAK AVERAGE The internal microcomputer flashes the instrument and front panel firmware version numbers and the GPIB address on the crt when the button is pressed The microcomputer also updates the GPIB primary address if the GPIB AD DRESS switches have been changed For another function of this button when in the talk only mode refer to Talk Only Listen Only Operation later in this section lt SHIFT gt PLOT If this button is pressed when the 494P is in the talk only or listen only mode see the TALK ONLY LISTEN ONLY switch descriptions later in this section it causes the 494P to send the appropriate commands over the GPIB to a plot ter connected to the bus The 494P display can be recreated on a TEKTRONIX 4662 or 4662 Opt 31 Interactive Digital Plotter or a 4663 in the 4662 emulation mode or a H
97. e GPIB has four elements mechanical electrical func tional and operational Of these four only the last is device dependent Operational elements state the way in which each instrument reacts to a signal on the bus MECHANICAL ELEMENTS The IEEE Std 488 defines the GPIB connector and cable assembly as the mechanical elements of the instrumentation system Standardizing the connector and cable assembly ensures that GPIB compatible instruments can be physically linked together with complete pin compatibility The connec tor has 24 pins sixteen active signal lines seven interlaced grounds and 1 shield connection Standard connector pin arrangement and nomenclature for the digital control signals are illustrated in Figure A 1 The cable that attaches to the GPIB connector must be no longer than 20 meters maximum with no more than fif teen peripheral devices including a GPIB controller con nected at one time The interconnecting cable assembly which is a standard accessory to the 494P is provided with both a plug and receptacle connector type at each end of the cable to allow either a star or linear bus structure Con nectors may be rigidly stacked using standard counter bored captive screws ELECTRICAL ELEMENTS The voltage and current values required at the connector nodes on the bus are based on TTL technology The power source is not to exceed 5 25 V referenced to logic ground The standard defines the logic levels as fol
98. e again Power up value SHORT TEXT change readout mode query 4415 45 Response to TEXT query 4415 45 5 7 Display Data and Crt Readout 1 O 494P Programmers UPRDO LORDO UPRDO upper readout and LORDO Jower readout queries Ce Cere0 Response to UPRDO and LORDO queries UPRDO a SP of 40 character srana ma Oaa LORDO 4415 48 4415 47 CHARACTER ASCII characters appear in the upper or lower row of regular crt readout Blanks are transmitted as spaces Regular readout that would be displayed if GPIB did not have control whether visible on the screen or not is the readout returned by the query not a message sent to the instrument by RDOUT With AVIEW and SAVEA both ON and BMINA and BVIEW both OFF the returned readout will be the saved readout Refer to the recall display com mand DRECAL in Section 4 5 8 Section 6 494P Programmers WAVEFORM PROCESSING INTRODUCTION The commands in this section refer to Table 6 1 allow local processing of spectrum data by the 494P microcomputer Some of these commands operate on a display data point This is an ordered pair an X and a Y value that corresponds to a point on the 494P display On command the 494P microcomputer acquires a display data point from the current digital storage waveform The point is heid in microcomputer memory until another command updates the data point A query requests that the 494P report the point Other
99. e data sent to the instrument to be lost One exception to the potential interaction just de scribed is when a Y as well as an X value is sent with the POINT command In that case since both values are es tablished by POINT the microcomputer does not read digital storage data into the buffer and the interaction does not occur 3 VRTDSP LIN interacts with FIBIG RGTNXT and LFTNXT because they transform linear data into logarithmic data before execution This interaction is not apparent un less the transformed data is output over the GPIB or loaded into digital storage because of either of the conditions noted in part 2 For further information refer to Multiple Use of Display Buffer for Waveform Processing and I O in Section 8 CENSIG TOPSIG center or move signal commands CENS Joe orso 4415 32 CENSIG center signal This command TUNES the frequency to center the signal represented by the display data point or as close as possible given the specified span accuracies TOPSIG move to top of graticule This command changes REFLVL to move the signal represented by the display data point to the reference level or as close as pos sible given the specified vertical display and reference level accuracies These commands do not acquire a new display data point or digital storage waveform Therefore if a new wave form is acquired after CENSIG or TOPSIG is executed the display data point may no longer match th
100. e message This REPEAT loop can be aborted by a DCL interface message Even though the microcomputer is busy executing the loop it recognizes DCL stops executing the message and flushes it from the input buffer t NOTE Use DCL to abort a REPEAT loop Pressing RESET TO LOCAL does not abort the loop It does however prevent execution of front panel commands if any in the loop which causes execution error status to be reported REPEAT can also be applied to a similar task keeping a signal centered as span division is reduced to focus on the signal Here s a routine that quickly spans down from 100 kHz to 10 kHz 100 REMARK SPAN DOWN 110 PRINT Z SIGSWP 120 PRI Z CEN SPA DEC SIG WAI POI 400 RGT 125 REP 5 Line 110 Guarantees the analyzer is in the single sweep mode This routine assumes the signal is already identified by the display data point as a result of FIBIG RGTNXT etc or POINT If the signal of interest is centered adding POINT 500 to the message in line 110 would do the job Line 120 Centers the signal steps the span down once arms the sweep and finds the signal in the new data A threshold value of center screen is used rather than video filtering to overcome noise in the data This speeds up the sweep but requires that the signal be less than four divi sions below the reference level The mnemonics in line 120 are squeezed to three letters to save space on the line
101. e signal of inter est Section 7 494P Programmers J SYSTEM COMMANDS AND QUERIES INTRODUCTION 494P device dependent message units are provided to set and return parameters of use to the controller in a GPIB system These commands and queries are listed in Table 7 1 and described in this section in three groups related to instrument parameters message execution and status and error reporting Table 7 1 DEVICE DEPENDENT COMMANDS AND QUERIES Function Message Unit Instrument Parameters SET Returns values of programmable parameters INIT Resets programmable parameters to power up values ID Returns model and firmware versions T Message Execution WAIT Synchronizes message execution with sweep REPEAT Repeats execution of previous units in message Status and Error Reporting EOS EOS Turns on off and queries end of sweep SRQ function RQS RQS Turns on off and queries RQS message function Status Byte Serial poll response DT DT Defines events triggered by GET EVENT Returns error condition reported in last serial poll byte ALLEV Ail events query NUMEV NUMEV Specifies fixed number of events returned in ALLEV EVQTY Specifies number of events returned in next ALLEV ERR Returns a code for the current error report ERCNT Returns the number of errors to be reported TEST Initiates self test routine 7 1 System Commands and Queries 494P Programmers SET INSTRUMEN
102. ed usually at 10 to 53 75 dB However the range may be 0 to 63 75 in the minimum noise mode 3 6 RDOUT Command 494P The remote to locai transition will always return RDOUT to NORMAL i e any messages sent to the crt via RDOUT commands will be replaced by the regular crt readout 492P If the remote to local transition occurs after UNT or UNL messages sent to the crt via RDOUT may be retained on the screen The regular crt readout will be re turned by changing any contro whose current condition is reported on the crt INIT Command 494P Whenever the INIT command appears in a pro gram it sets TIME DIV to the front panel setting If INIT is sent when TIME DIV is at a setting that is not compatible with the following input e g a high 1 ps sweep speed the processor will recognize that an uncalibrated condition oc curred and an uncal error message will be issued Including a new TIME DIV setting in the input will not alone eliminate this To get around the error message SRQ must be turned off before INIT is sent for example RQS O INI TIM AUT MIN O ERR RQS 1 492P If a TIME DIV setting is included in an INIT statement no SRQ will be issued for example INI TIM AUT MIN O REV FEB 1984 Section 4 494P Programmers FRONT PANEL CONTROL INTRODUCTION Commands and queries for front panel control refer to Figure 4 1 are grouped in this section according to the following seven
103. ed for at least 100 us ws The Controller function has specified time intervals for certain operations For example the execution time for par allel polling instruments on the bus cannot be less than 2 us If the controller is in the controlier active wait state and does not receive an internal message to conduct a parallel poll it must wait for at least 1 5 us before going to the controller active state This gives the NRFD NDAC and EOI lines sufficient time to assume their valid states The controller must also have a delay of at least 2 us 1 1 xs for tri state drivers in order for the instruments to see the ATN line asserted before the controller places the first data byte on the bus Taking Control Asynchronous or Synchronous All data bytes transmitted over the GPIB with the ATN line asserted are interpreted as system control information Asserting ATN directly at any moment is an asychronous operation with respect to the bus and may cause loss of data if a handshake cycle is in progress To prevent loss of data a controller can take control synchronously that is it can monitor the Transfer Bus and only assert ATN when DAV is unasserted false Passing Control As a controller in charge the system controller program may relinquish control to any other instrument in the system capable of acting as a controller The controller in charge first addresses the other controller as a talker and then sends the TCT Ta
104. emented the function DCL Device Clear Function The DCL Device Clear function ailows the controller in charge to clear any or all instruments on the bus The controller under program direction asserts ATN and sends either the universal DCL Device Clear command or the SDC Selected Device Clear command A 12 When the DCL message is received ail instruments on the bus must clear or initialize their internal device functions When the controller sends the SDC command only those instruments that have been previously addressed to listen must respond The IEEE 488 standard does not specify the settings an instrument must go to as a result of receiving the DCL or SDC command in general these commands are used only to clear the GPIB interface circuits within an instrument DT Device Trigger Function The DT Device Trigger function allows the controller in charge to start the basic operation specified for an instru ment or group of instruments on the bus The IEEE 488 standard does not specify the basic operation an instrument is to perform when it receives the GET Group Execute Trig ger command To issue the GET command the controller asserts ATN sends the listen addresses of the instruments that are to respond to the trigger and then sends the GET message Once an instrument starts its basic operation in response to GET the instrument must not respond to subsequent trigger state transitions until the current
105. er attempts to execute the remainder of the message after local control is restored At that time com mands that attempt to change a front panel function will result in error SRQs because they conflict with local control The response of the 494P to interface messages de pends on the manner in which they are handled Some inter face messages are handled by the GPIB interface while others require action by the microcomputer The latter gen erally involve the 494P GPIB address and are implemented in microcomputer firmware rather than on the interface The speed with which these commands can be handshaked de pends on how fast the microcomputer can service the re sulting interrupt which in most cases should be within a few hundred us The following considerations apply to interface mes sages received by the 494P 1 Universal commands LLO SPE and SPD are handshaked and acted on by the interface so they are unaf fected by the microcomputer s activity The serial poll pro ceeds without delay if the talk address follows since this function is handled by the interface 2 UNL and UNT are handshaked by the interface which immediately resets the talk or listen function if active Ad dresses that do not match those set by the rear panel switches are handshaked and discarded by the interface System Commands and Queries 494P Programmers Status Byte When the current talk or listen address MTA or MLA is decoded by the inte
106. er local control Parallel Poll PP1 The 494P responds to a parallel poll to indicate if service is requested Device Clear DC1 The 494P responds to the DCL device clear and SDC selected device clear interface messages by resetting its input and output buffers to restart bus communications When these messages are executed they clear outstanding SRQ conditions and set the ERR query response to zero Power up status if selected internally is an exception see Status Byte in Section 7 for more on power up status and for the effect of busy status on the execution of DCL and spc Device Trigger DT1 The 494P device trigger function is implemented so the group execute trigger GET message causes the instrument to abort the current sweep and rearm for the new sweep The new sweep begins when the triggering conditions are met The DT command must be on and the 494P must be in the Remote mode for GET to have any effect Controller CO The 494P does not act as a controller 17 introduction to GPIB Operation 494P Programmers CONNECTING TO A SYSTEM The 494P can be connected directly to a GPIB system with the cable supplied with the instrument The IEEE STD 488 PORT is shown in Figure 1 6 To avoid interference on the bus connect the 494P after turning on power or while the controlier on the bus is turned off The GPIB is a flexible system that works either in a star or linear configuration as shown in Figure 1 7
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108. ft ware routines which instrument will talk and which instru ments will listen during any given time interval The con troller has the ability to assign itself as a talker or a listener whenever the program routine requires it In addition to des ignating the current talker and listeners for a particular com munication sequence the controller is assigned the task of sending special codes and commands called interface con trol messages to any or ali instruments on the bus A com plete operating system may contain more than one controller The IEEE standard has provisions for a system controller that operates with another controller in charge of the bus The controller that is in charge of the bus can take control only when it is directed to do so by the system con troller The system controller itself may be but is not neces sarily the controller in charge of the bus INTERFACE CONTROL MESSAGES The two types of interface control messages are multi line messages sent over the data bus and uni line mes sages A message that shares a group of signal lines with other messages in some mutually exclusive set is called a multi line message Only one multi line message message byte can be sent at one time A message sent over a single line is called a uni line message two or more of these mes sages can be sent concurrently Only multi line messages are discussed here uni line messages are discussed later under GPIB Signal Line
109. fter a large center frequency change more than a few 100 MHz oscillator drive will cause center frequency er rors This is especially noticeable using slow sweep speeds when the time is long between the end of sweeps and the frequency corrections Thus delay time in addition to that built into the 494P may be needed to allow the oscillator drift to reduce in magnitude USING REPEAT FOR SIGNAL TRACKING AND SEARCHES The REPEAT command adds another dimension to 494P messages the number of times to loop through a string of commands or queries Several uses are suggested here Tracking a Signal The 494P can track a signal while keeping it centered on the display To do this the 494P updates its frequency At the same time waveform processing is used to find the peak value after each sweep and center it on the display The REPEAT command causes the 494P to execute the waveform processing message repeatedly 100 REMARK TRACK A SIGNAL 110 PRINT Z WAIT FMAX CENSIG SIGSWP REPEAT 1056 8 10 Line 110 Causes the microcomputer to wait until the sweep is completed before it processes the digital storage waveform then it arms the sweep to acquire a new wave form This WAIT SIGSWP sequence does not hang the first time through the loop even if a sweep is not in progress or the instrument is not in single sweep mode see WAIT in Section 7 for more details The REPEAT command causes the microcomputer to continue to execute th
110. go to local to be executed precede the decimal code with the 494P listen address The codes for the addressed commands are 1 for GTL 5 for PPC parallel poll configure and 8 for GET group execute trigger GET causes the analyzer to abort the current sweep and immediately start another sweep synchronizing data acquisition with the interface message When the IFC line is asserted by the controller as when the BASIC statement INIT is executed the 494P talker and listener functions are initialized same effect as UNT and UNL 4050 Series Controller Use the WBYTE statement to send the universal commands 100 WBYTE 20 For addressed commands precede the decimal code with the 494P listen address 100 WBYTE L 1 63 where L GPIB address 32 CP1100 and CP4100 Series Controllers Use the SIFCOM statement to send the commands en tering the mnemonic for the interface message 100 SIFCOM N LZ GTL REV MAR 1985 Getting Started 494P Programmers 9826A Controller For the 9826A use commands that transfer the interface messages For example cir sends DCL trg7 sends GET Icl701 sends GTL to the device with primary address 1 and 07 sends LLO The RESET statement asserts IFC LZ is the 494P listen address and is necessary only for addressed commands The SIFLIN statement is used to as sert IFC ACQUIRING A WAVEFORM The waveform in digital storage can be requested as ei ther ASCll coded decimal num
111. he GPIB system can be in the active talker state at any given time A non controller commences talking when ATN is released and continues its talker status until an Interface Clear IFC message occurs or an Untalk UNT command is received from the controller in charge The instrument will stop talking and listen any time that the controller in charge asserts ATN One or more instruments on the bus can be programmed for the L Listener function by use of their specific primary listen address called MLA Some of the instruments inter faced to the bus may be programmed for the LE Listener Extended function if implemented The LE function re quires a two byte address code No L or LE function is ac tive during the time that ATN is asserted All talker and listener functions must respond to ATN within 200 ns They must also respond to IFC in less than 100 ps A 71 IEEE STD 488 GPIB System Concepts 494P Programmers An instrument may be a talker only a listener only or implement all functions in any case its address code has the form XiOTTTTT for a talker and XO1LLLLL for a lis tener For instruments with both T and L functions the T bit binary values are usually equal to the binary value of the L bits Before applying power to the system the system oper ator sets these five least significant bits by means of an address switch on each instrument The controller s ad dress code may be implemented in software The system
112. he percent sign in line 540 instructs the controller to use the alternate delimiter for H This maneuver inputs the header in the 494P response CURVE CRVID FULL and stops at the block binary delimiter which is discarded Line 550 Makes the 494P a talker 8 4 Line 560 First inputs the initial two bytes in the block binary format the byte count into A and B This routine does not make use of the byte count but could be ex panded to count the bytes as an error check Line 560 next inputs the binary waveform data to fill array W The RBYTE statement completes by inputting the check sum into D Statements could be added to this routine to keep a running 8 bit sum of the bytes in the binary block such a sum could be added to the check sum byte as an error check two added together disregarding the carry should equal zero Line 570 Untalks the 494P Sending a Binary CURVE to the 494P The following routine employs end block format to trans fer a waveform to the 494P Array W is transferred if not already created by the preceding routine W should be di mensioned to 1000 and filled with data in the range 0 to 255 600 REMARK SEND BINARY CURVE TO 494P 610 WBYTE 33 64 W 255 620 WBYTE 63 Line 610 Sends the 494P listen address followed by the binary number for 63 which is the ASCII code for the end block delimiter Line 610 then sends the binary numbers in array W after which it asserts EOI asserted concurrent
113. heir use are found in Section 8 To get started getting smarter here is a simple application 4050 Series Controller The following 4050 Series program catalogs the first 10 harmonics of the CAL OUT signal If the instrument is set to other than the power up state precede the program with the INIT command As in the other 4050 Series programs in this manual Z is the variable that holds the value of the 494P GPIB address switches 90 PRINT Z INIT 100 REMARK CATALOG ROUTINE 110 PRINT 2Z SPAN 1 MHZ REFLVL 20 DBM VIDFLT NARROW SIGSWP 120 FOR I 1 TO 10 130 PRINT Z FREQ 1 1 0E 8 SIGSWP WAIT 140 PRINT Z FIBIG TOPSIG FREQ REFLVL 150 INPUT 2 R 160 PRINT SIGNAL I R 170 PRINT Z REFLVL 20 DBM 180 NEXT I Line 110 Sets span div and reference level for the start of the signal search and selects narrow video filter to smooth the data for the routine The single sweep mode is selected so new data can be acquired on command Line 120 Starts the loop Line 130 Tunes to a harmonic of the calibrator signal then starts a sweep to acquire new data The WAIT guaran tees digital storage is filled with updated data before proceeding Line 140 FIBIG finds the calibrator harmonic it should be the only signal on screen TOPSIG automatically changes analyzer gain or input attenuation to bring the sig nal peak to the reference level top of screen These and other wavefo
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115. inator it executes the commands in the message in the order they were received The 494P remains busy until it is done executing the com mands in the buffer unless the process is aborted by the DCL Device Clear or SDC Selected Device Clear interface messages While busy further input is not accepted see Status Byte in Section 7 for more on busy status Output if requested is begun only after the entire input message is executed Because display measurement data input and output and waveform processing share the same buffer conflicts can arise This is discussed in the Interaction part of the CURVE command in Section 5 under Display Data Point Commands Interaction in Section 6 and is further expanded on under Multiple Use of Display Buffer For Waveform Pro cessing and WO in Section 8 Command Format A command message unit either sets an operating mode or parameter or it transfers display data to the instrument The command format to set a mode or parameter includes the following possible paths COMMAND none J FORMAT 2 FORMAT TERM CHARACTER CHARACTER J ofauenv SS a 4415 51 Because the general command format for display data transfers is complicated it is omitted see the data 1 0 com mands in Section for the specific command syntax i i ow Device Dependent Message Structure and Execution 494P Programmers Header Header elements are mnemonics that repre
116. ing This limitation also relates to phase or frequency noise It may be neces sary to transfer the entire waveform and process these sig nals externally Two other factors affect how the signal finding com mands perform The first is separation Because the shape of the signal response is an important factor a definite notch must be present between adjacent signals for both to be recognized The second factor is noise Because the sig nal search routine is sensitive enough to detect small sig nals it also detects noise peaks that appear to be small signals Both of these factors are subject to your control so you can improve the results of waveform processing by practicing the following suggestions Once a signal is found the analyzer can be instructed to change its center frequency to match the signal at the dis play data point The analyzer can also be instructed to change its reference level to match the amplitude of the sig nal at the display data point The commands that do this CENSIG and TOPSIG rely on the span division and vertical display scale factors when computing how far to change the center frequency and reference level respectively The ac curacy of span division and vertical display along with the accuracy of REFLVL determine how closely the signal peak is moved to the center and top of the graticule You may apply the waveform processing commands again for greater accuracy Acquiring Data for Waveform Proce
117. interrupt 492P Interface messages are processed despite busy status if the busy status occurs because the microprocessor is executing a WAIT command If RTL interrupts WAIT the microcomputer attempts to execute the remainder of the message after restoring local control and waiting for EOS If the busy status occurs because the microcomputer is executing any device dependent message other then WAIT the response is handled the same as described for the 494P GET Group Execute Trigger 494P GET requires microcomputer action so hand shake occurs only when the microcomputer can handle the interrupt The effect of GET is masked by DT Device Trigger 492P Handshake occurs only when the micro computer is not executing a device dependent message unit other than WAIT GET is not masked 3 5 Device Dependent Message Structure and Execution 494P Programmers EVENT ERR Codes 494P Bit 5 refiects the current condition and a serial poll clears the EVENT status that was reported Only one Command Error is saved i e the category code of the first Command Error will be reported and any succeeding Com mand Errors will be ignored All errors from other catego ries Execution Errors Internal Errors System Events Execution Warnings and Internal Warnings are saved and reported Refer to Section 7 for information on the 494P Status and Error Reporting 492P Bit 5 reflects the current condition and a seria
118. ints 494P Programmers Table 8 2 TRANSFER TIMES eee S 1 ais Transfer 4041 i 4051 4052 Data Output SET response 480 ms 480 ms 480 ms CURVE response Binary input as numbers 2 26s 2 6s 830 ms ASCII input as a string 71s 74s 7is ASCII input as numbers 95s 11s 7 8 s Display Data Input CURVE Binary from number array 1 45 jt1is 1 14s ASCII as a string 95s 81s j81s ASCII as numbers 124s 20 0s 11 5s 8 15 Appendix A 494P Programmers IEEE STD 488 GPIB SYSTEM CONCEPTS INTRODUCTION The General Purpose Interface Bus GPIB is a digital control bus that allows efficient communications between self contained instruments or devices interconnected in an instrumentation system The GPIB is an interface system independent of the stimulus or measurement functions in corporated in any instrument Instruments or devices designed to operate on the digital control bus must be developed according to the specifica tions contained in IEEE Std 488 1978 IEEE Standard Digi tal interface for Programmable Instrumentation At Tektronix the IEEE 488 digital interface is commonly known as the General Purpose Interface Bus GPIB This section discusses the basic concepts of the GPIB For complete specifications refer to the IEEE Std 488 1978 standard published by the Institute of Electrical and Electronics Engi neers Inc 345 East 47th Street New York New York 10017 Th
119. ions are added to do some spectrum analysis locally The IEEE Std 488 General Purpose Interface Bus GPIB port added in the 494P allows it to be used with a wide variety of systems and controllers This versatility is accom plished because the 494P is implemented according to the Tektronix Interface Standard for GPIB Codes Formats Conventions and Features This standard promotes ease of operation and makes the 494P compatible with other Tektronix instruments and as much as possible with GPIB instruments from other manufacturers NOTE Some of the lines of input in examples of controller programs in this section extend beyond the column width limitations Where this occurs the overrun in formation is indented on the immediately following line important whenever a line is broken it is always where a natural space occurs So be sure to add a space when inputting the program GPIB CONTROLS AND INDICATORS Figure 1 1 RESET TO LOCAL button TERTIEAC peo oita DISBLAY PITER 5 1 fh ADDRESSED pata ERY REFERENGE LEVEL MIN BF AT TEN a5 4415 01 Figure 1 1 GPIB control and indicators 1 1 Introduction to GPIB Operation 494P Programmers RESET TO LOCAL REMOTE This button is lighted when the analyzer is under control of the GPIB controller While under remote control the other 494P front panel controls are not activ
120. is armed Power up value Off Interaction Any TRIG command cancels the single sweep mode SIGSWP single sweep query 4415 171 Response to SIGSWP query 4415 172 The response to the SET query is omitted if single sweep is not active see SET under System Commands And Que ries Section 7 4 26 Kop TIME time div command 4415 173 NUM 1 2 5 sequence in the range 2006 to 10 Num bers not in this sequence are rounded to the nearest step AUTO The 494P microcomputer is requested to select the fastest sweep allowed for calibrated response INC or DEC The sweep rate is changed 1 in the sequence if possible MAN The sweep is coupled to the MANUAL SCAN control so the operator can manually scan the spectrum As the control is rotated the horizontal position of the crt beam and the analyzer front end tuning are varied from the center of the sweep and the center of the selected spectrum Cor rection of the center frequency is done periodically EXT The sweep is coupled to EXT IN HORIZ on the 494P rear panel The horizontal position of the crt beam and the analyzer front end tuning are varied by an external sig nal A signal in the range 0 to 10 V scans the spectrum Correction of the center frequency is done periodically Power up value TIME DIV control setting Interaction Too fast a sweep speed for a given reso lution bandwidth will uncalibr
121. is turned off Refer to the ON description for operation with SAVEA off If both waveforms are turned off the input signal is displayed in real time NUM 1 equals ON numbers 0 5 are rounded to 1 Number 0 equals OFF numbers less than 0 5 are rounded to 0 Power up value Both A and B on AVIEW and BVIEW A and B waveform display queries 4415 177 Response to AVIEW and BVIEW queries 4415 478 Front Panel Control 494P Programmers AVIEW BVIEW SAVEA SAVEA save A waveform command 4415 179 ON The A waveform updating is discontinued and the current contents are saved This allows comparison with the B waveform which is continuously updated The informa tion in the crt readout is saved and will be displayed instead of the current analyzer settings if only AVIEW is on both BVIEW and BMINA off OFF The A waveform updating is resumed NUM 1 equals ON numbers gt 0 5 are rounded to 1 Number 0 equals OFF numbers less than 0 5 are rounded to 0 Power up value Off Interaction BMINA ON turns SAVEA ON SAVEA OFF turns BMINA OFF SAVEA save A waveform query COLON 4415 180 Response to SAVEA query EDH 4415 1814 4 29 Front Panel Control 494P Programmers BMINA DSTORE DRECAL BMINA B A waveform display command ee be no ON The 494P microcomputer turns on SAVEA and then turns on a display of the difference between the A wavefo
122. ity to provide more detailed information on errors related to ab normal status conditions One query TEST checks the 494P ROMs and RAM EOS end of sweep command 4415 66 ON The analyzer asserts SRQ if RQS is ON when a sweep completes OFF The analyzer does not assert SRQ for the EOS conditon NUM 1 equals ON numbers 0 5 are rounded to 1 0 equals OFF numbers less than 0 5 are rounded to 0 Power up value Off Interaction EOS is always OFF in the talk only and listen only modes EOS end of sweep query 4415 67 Response to EOS query 4418 68 RQS request service command 4415 69 ON SRQ is asserted when abnormal status conditions occur OFF SRQ is not asserted is masked when abnormal status occurs NUM 1 equals ON numbers 0 5 are rounded to 1 0 equals OFF numbers less than 0 5 are rounded to 0 Power up value On Interaction RQS is always OFF in the talk only and listen only modes RQS request service query 4415 70 Response to RQS query Cras J6 4415 71 7 5 System Commands and Queries 494P Programmers Status Byte Status Byte response to serial poll 87654321 Decimal Condition 010X000 1 6581 Power on 0 X0XO0OQ 1 0 2 18 66 82 End of Sweep 0000X0000 0 16 Ordinary operation oxX1x0o001 33 49 97 113 Command error oxX1x0010 34 50 98 114 Execution error oxX1xo01 Ff 35 51
123. ke Control command The other control ler then becomes the controller in charge when ATN is re leased Performing A Serial Poll The controller in charge may conduct a seriai poll at any time whether or not an instrument on the bus has asserted the SRQ line Most but not ali instruments have the Ser vice Request SR function To perform a serial poll the controller first asserts ATN and issues the Untalk UNT and Unlisten UNL commands The controller then sends the Serial Poll Enable SPE com mand followed by the talk address of the first instrument to be polled The controller then releases ATN and the ad dressed talker responds by sending its status byte over the bus If the addressed talker has requested service it must assert bit seven of the status byte and encode the remaining seven bits to indicate the reason for asserting SRQ Status bytes are device dependent and are not specified in the IEEE 488 standard An addressed instrument will release its SRQ line when serial polled but other instruments may still IEEE STD 488 GPIB System Concepts 494P Programmers hold it asserted When the controller has read the status byte of an addressed instrument it reasseris ATN and ad dresses the next instrument to talk then releases ATN and receives the instrument s status byte The routine continues until the controller no longer detects the SRQ line asserted At this time the controller should send the Serial Poll Dis
124. l poll clears the ERR status that was reported All errors regardless of category are saved Preserving Frequencies 494P Band changes will attempt to preserve oscillator frequencies They will set to a band limit if the oscillator frequencies would cause an out of band center frequency If a 494P is not tuned after a band change and is returned to the original band the center frequency will be the same as that before the band changes 492P The original center frequency will not be pre served The 492P will just check to see if the oscillator fre quencies will cause an out of band frequency or not MINATT Command 494P MINATT always set from MAXPWR by limiting the power at the first mixer to 18 dBm 492P MINATT set using 10 dBm for non preselected band and 18 dBm for the preselected bands Reference Level 494P The minimum reference level is 123 dBm The A amplitude range is 63 75 dB and slides depending on the reference level when the A amplitude mode is entered The range slides from a 10 to 57 75 range to a 19 to 38 75 dB range If the entry level is on a 10 dB step the range is 0 to 57 75 dB If the entry level is not on a 10 dB step the range is next 10 dB step entry level to 57 75 dB lower e g entering A amplitude at 19 dBm will cause the range to be 9 00 to 48 75 dB 492P The minimum reference level is 123 dBm The A amplitude range is 63 75 dB and fix
125. l of 0 dBm The WFMPRE portion of the SET response includes only the WFID and ENCDG arguments 5 4 CURVE display curve command CRVID The destination A B or full is selected for the waveform being sent If this argument is omitted the last CRVID in a CURVE command or WFID in a WFMPRE com mand takes precedence A or B indicates a 500 point trans fer FULL indicates 1000 points 4415 38 NUM This is a sequence of ASCIl coded digits delim ited by commas between successive numbers BINARY BLOCK Binary block is a sequence of binary numbers that is preceded by the ASCII code for percent and a two byte binary integer representing the number of binary numbers plus one the extra byte is the checksum and followed by the checksum The checksum is the 2 s complement of the modulo 256 sum of all preceding bytes except the first Thus the modulo 256 sum of all bytes except the first should equal zero to provide an error check of the binary block transfer END BLOCK End block is a sequence of binary num bers that is preceded by the ASCII code for at EOI must be asserted concurrently with the last data byte The end block can only be the last data type in the message Example CURVE CRVID FULL 100 100 101 99 lt 996 more numbers gt CURVE lt 500 or 1000 numbers gt CUR lt BINARY BLOCK gt interaction A waveform sent in a CURVE command is overwritten in the display
126. le while use of codes and data formats is encouraged to make maximum use of bus capabilities To make 494P messages easy to understand and write ordinary engineering terms are used Message mnemonics are chosen to be short yet remind the user of their function For example to set the 494P center frequency to 500 000 MHz the message FREQ 500 000 MHZ could be sent over the bus after the 494P has been addressed as a listener Variations on this message are allowed to make it shorter or send the frequency in scientific notation but this example shows the conversational format of 494P mes sages that makes them readable therefore human oriented The 494P device dependent messages are upward compatible with the 492P except as noted later under 494P 492P Compatibility SYNTAX DIAGRAMS 494P messages are presented in this manual in syntax diagrams that show the sequence of elements transferred over the bus Each element is enclosed in a circle oval or box Circles or ovals are used to contain the mnemonics for literal terminal entry elements i e a character or string of characters that must be sent exactly as shown Because most mnemonics may be shortened the command and query characters required in a 494P literal element i e the first three characters of the element are shown larger than optional characters Although mnemonics are shown all up per case the 494P accepts either upper case or lower case ASCII characters Query
127. licts 8 8 Finding Signals with 494P Waveform PROCESSING wai EENE KEEA EEA 8 9 Understanding how Waveform Processing Works 8 9 Acquiring Data for Waveform Processing 55 8 9 Spectrum Search 8 9 Measuring Signal Frequency with COUNT 20 e033 oedees reed 8 10 eel Section 8 494P Programmers TABLE OF CONTENTS cont Page HELPS AND HINTS cont Using COUNT CF 8 10 Higher Center Frequency Drift Rate After Tuning 8 10 Using REPEAT for Signal Tracking and SearChOs 5h rapiro aAA ss 8 10 Tracking a Signa 8 10 Spectrum Search Using REPEAT 8 11 Messages on the Crt Using RDOUT 8 12 Using CAL Over the Bus 8 12 Comparing the Status Byte and the ERR EVENT Response 8 13 Firmware Operating Notes 8 13 Execution and Transfer Times 8 14 Appendix A IEEE STD 488 GPIB SYSTEM CONCEPTS INtODUCH ON Ga54 Beste A TAT A 1 Mechanical Elements A 1 Electrical Elements A 1 Functional Elements A 2 A Typical GPIB System A 3 Talkers Listeners and Controllers A 6 Interface Control Messages A 6 REV MAR 1985 Page Appendix A IEEE STD 488 GPIB SYSTEM CONCEPTS cont Device Dependent Messages AS GPIB Signal Line Definitions A 8 Transfer Bus Handshake A 8 Management Bus
128. line of a help mes sage All help messages are sent in sequence by this HELP ma command 4415 197 4 34 STORE store settings command x stone J E num je 4415 199 NUM The 494P control settings are loaded into the selected battery powered memory range is 0 9 Power up value The 494P automatically STOREs its power down settings in memory 0 when the power is turned off overwriting previously stored settings in memory 0 There is no STORE query RECALL recall settings command RECALL SP e NUM 4415 200 NUM The 494P control settings are recalled from the selected battery powered memory range is 0 9 Power up value The 494P automatically STOREs its power down settings in memory 0 when the power is turned off overwriting previously stored settings in memory 0 There is no RECALL query Front Panel Control 494P Programmers STORE RECALL PLOT PLOT plot data query RRO 4415 201 PLOT sends information to plot the 494P display on the TEKTRONIX 4662 or 4662 Opt 31 Interactive Digital Plotter or the 4663 in the 4662 emulation mode or the Hewlett Packard HP7470A Plotter The response to PLOT depends on the plotter in use NOTE Since the GPIB languages of the 4662 4662 Opt 31 and 4663 Interactive Digital Plotters or the HP7470A Plotter do not conform to the Tektronix interface Standard for GPIB Codes Formats Conventions and Features thi
129. lowed to assert ATN ATN is asserted when an instrument connected to the bus is being enabled as a talker or listener or when sending other interface con trol messages As long as the ATN line is asserted low only instrument address codes and interface control mes sages are sent over the bus When the ATN line is unasserted only those instruments enabled as a talker and listener s can send and receive data over the bus A 10 SRQ Service Request Any instrument connected to the bus can request the controller s attention by asserting the SRQ line The controller responds by asserting ATN and executing a serial poll routine to determine which instrument is requesting service The instrument requesting service re sponds with a device dependent status byte with bit seven asserted When the instrument requesting service is found program control is transferred to a service routine for that instrument When the service routine is completed program controli returns to the main program The controller does not have to see the SRQ line asserted to perform a polling routine it may do so whenever a program requires it REN Remote Enable The system controller asserts the REN signal line whenever the interface system operates un der remote program control Used with other interface con trol messages such as LLO Local Lockout or GTL Go To Local the REN signal causes an instrument on the bus to select between two alternate sources of
130. lows 1 Logical 1 is a true state low voltage level lt 0 8 V signal line is asserted 2 Logical 0 is a false state high voltage level 2 2 0 V signal line is not asserted Messages can be sent over the GPIB as either active true or passive true signals Passive true signals occur at a high voltage level and must be carried on a signal line using open coliector devices Active true signals occur at a low voltage level A 1 IEEE STD 488 GPIB System Concepts 494P Programmers LOGIC GND GND 10 4415 21 Figure A 1 IEEE Std 488 GPIB connector FUNCTIONAL The functional elements of the GPIB cover three areas 1 The ten major interface functions of the GPIB are listed in Table A 1 Each interface function is a system ele ment that provides the basic operational facility through which an instrument can receive process and send mes sages over the GPIB ELEMENTS 2 The second functional element is the specific protoco by which the interface functions send and receive their lim ited set of messages 3 The logical and timing relationships between allowa ble states for all interface functions is the third area covered Table A 1 MAJOR GPIB INTERFACE FUNCTIONS interface Function Symbol Source Handshake SH Acceptor Handshake AH Talker or Extended Talker TorTE Listener or Extended Listener Lor LE Service Request SR Remote Locai RL Parallel Poll PP Device Clear DC Device Trigge
131. ly with 255 a byte with all bits set to one EOI causes the 494P to act on the message The CURVE header is omitted it is not required but would be accepted if sent The 494P buffers the last byte hex FF but does not put it into digital storage Line 620 Sends UNL j f Ei Helps and Hints 494P Programmers SCALING SAVING AND GRAPHING WAVEFORM DATA The 494P waveform data outputs numbers from 0 to 255 called screen units These numbers can be scaled to elec trical units using data contained in the WFMPRE response Here is an expanded version of the 494P binary output program given previously This version transfers whatever portion of memory you have specified with a WFMPRE command A B or FULL power up default is FULL The program scales both the X and Y values and stores them in a two wide array The program also saves the n scaled bi nary array so you can transfer it back into 494P digital stor age if you wish 500 REMARK GET AND SCALE 494P BINARY CURVE OUTPUT 510 DELETE W M 520 PRINT Z WFMPRE ENC BIN WFMPRE CURVE 530 PRINT 37 0 37 255 255 540 INPUT 1 N X3 X2 X1 3 2 1 550 DIM W N M N 2 560 WBYTE 65 570 RBYTE A B W D 580 WBYTE 95 590 FOR I 1 TON 600 M I 1 X1 X2 I 1 X3 610 M I 2 Y1 2 W I 3 620 NEXT I Line 510 Clears the waveform arrays Line 520 Requests the waveform preamble and a binary curve Line 530 Sets the alter
132. mand 4415 100 This command allows the 494P frequency control loop to be disabled for diagnostic purposes It also allows a fallback to low accuracy center frequency operation if the frequency control loop fails ON Center frequency corrections are disabled OFF Center frequency corrections are enabled NUM 1 equals ON numbers gt 0 5 are rounded to 1 Number 0 equals OFF numbers less than 0 5 are rounded to 0 DISCOR disable frequency corrections query 4415 101 Response to DISCOR query ewo o 4415 102 4 6 FRQRNG frequency range command 4415 103 NUM The analyzer accepts number arguments in the range of 1 through 12 and changes the frequency range accordingly Non integer values are rounded if the number is too large or too small the analyzer maintains its current frequency range and reports an error INC The analyzer changes to the next higher fre quency range if possible DEC The analyzer changes to the next lower fre quency range if possible Power up value Frequency Range 1 Interaction The 494P microcomputer automatically selects the lowest frequency range that encompasses the frequency setting that responds to the FREQ command FRQRNG frequency range query i 4445 404 Response to FRQRNG query Ga 4415 105 oo a COUNT counter command oa Con AN NUM 4415 106 ON The counter
133. maximum position NUM 0 equals KNOB numbers less than 0 5 are rounded to 0 1 equals PEAK numbers gt 0 5 and less than 1 5 are rounded to 1 Number 2 equals AVG num bers 1 5 are rounded to 2 Interaction Averaging can reduce the value in digital storage for signals with very narrow response or pulsed signals Power up value Knob CRSOR peak average cursor query EO 4415 191 Response to CRSOR query ef e 4415 192 4 31 Front Panel Control 494P Programmers DISPLAY CONTROL Figure 4 7 These commands control the 494P crt display functions and clip the baseline trace CLIP Refer to Table 4 5 Each to dispiay the readout REDOUT light the graticule GRAT function can be turned on or off and queried Tektronix A ASAA at Sronace rr G a oo 4 A 0 0 ian at m2 O FREQUENCY gy RESOLUTION osma enay Eros D anomia REFERENCE LEVEL S MIN AF ATTEN 38 ian S amom oe umuone owen LEa oono a Fe 8 6 3 OF oro POSIT oureet SARER ay Q franses Figure 4 7 Front panel Display Control commands 4 32 Faas J y Front Panel Control 494P Programmers Display Control Display control command f MNEMONIC SP 4415 193 Table 4 5 DISPLAY CONTROL Mnemonic ON OFF Power up Value REDOUT Display instrument control characters Blank readout On
134. mmedi ately accessible as one reads the marking or a hazard to property including the equipment itself DANGER indicates a personal injury hazard immediately accessible as one reads the marking SYMBOLS In This Manual A This symbol indicates where applicable cau tionary or other information is to be found As Marked on Equipment DANGER High voltage Va Protective ground earth terminal A ATTENTION refer to manual Refer to manual PRECAUTIONS Power Source This product is intended to operate from a power source that will not apply more than 250 V rms between the supply conductors or between either supply conductor and ground A protective ground connection by way of the grounding conductor in the power cord is essential for safe operation Grounding the Product This product is grounded through the grounding conduc tor of the power cord To avoid electrical shock plug the power cord into a properly wired receptacle before connect ing to the product input or output terminals A protective ground connection by way of the grounding conductor in the power cord is essential for safe operation ee Danger Arising From Loss of Ground Upon loss of the protective ground connection all acces sible conductive parts including knobs and controls that may appear to be insulating can render an electric shock Use the Proper Power Cord Use only the power cord and co
135. n P before using it for example O dim P 15003 Summation Whatever the controller input statement the actions shown in the syntax diagram below must be taken to re ceive a message from the 494P The syntax diagram to receive a message could be ap pended to the end of the one shown to send a message Together they describe the two steps necessary to obtain output from the 494P The message in the first diagram would include the query and the response in the second diagram would come from the 494P to answer that query gt a 494P QUERY tlt RESPONSE EAN OUTPUT UNL amp ATN 4415 87 ad Getting Started 494P Programmers EXERCISE ROUTINES LISTEN TALK Now let s put the statements for message l O together to exercise the 494P as a listener and a talker This routine is handy because it waits for your input and sends it time after time If the 494P responds with a message the message is printed before another message is requested from you En ter any of the commands or queries described in Sections 4 through 7 The HELP query wiil return an alphabetized list of the available commands and queries An SRQ handier is included to print out any error messages The following routines make use of one of the friendly features of the 494P When the 494P is talked with nothing to say it outputs a byte with all bits set to one and asserts EOI The routine doesn t have to search the output cha
136. n on procedure the signal peak should occur vertically at the reference level and horizontally at the graticule center if not refer to the Initial Turn On procedure in either the 494 494P Operators Manual or 494 494P Operators Handbook or better yet try the automatic CAL function provided and described in the Operators manual and handbook If you receive an SRQ message on the screen of the 4050 Series controller add a SRQ handler sequence to the program This sequence can be added to any 4050 Series program example shown in this manual The amended pro gram would took like the following 2 2 90 ON SRQ THEN 140 100 PRINT Z FREQ 100 MHZ 110 PRINT Z SPAN 1 MHZ 120 PRINT Z REFLVL 20 DBM 130 POLL Q1 Q2 Z 140 PRINT SRQ Q2 150 RETURN or 90 ON SRQ THEN 110 100 PRINT Z FREQ 100 MHZ SPAN 1 MHZ REFLVL 20 DBM 110 POLL Q1 Q2 2 120 PRINT SRQ Q2 130 RETURN CP1100 and CP4100 Series Controllers The story is the same for two other Tektronix controllers Only the names change for the I O statements With TEK SPS BASIC in Tektronix CP1100 and CP4100 Series Con trollers the output statement is PUT 100 PUT FREQ 100 MHZ SPAN 1 MHZ REFLVL 20 DBM INTO N LZ where N is the number of the GPIB interface in the controller and LA is the 494P listen address primary address plus 32 9826A Controller For the Hewlett Packard 9826A Desktop Computer use the write statement
137. n or display If a video filter VIDFLT is switched in noise in the display is reduced Calibration of the IF filters for frequency and amplitude is possibie from the front panei CAL Viektronix 494P OS iran FREQUENCY BiaTEAL STORAGE FREQUENCY gy RESOLUTION SPANO O Banowioth 3 b exennas MEA in ATERI OUTPUT Mixa e Figure 4 4 Front panel Vertical Display and Reference Level commands 4 15 Front Panel Controi 494P Programmers VATDSP VRTDSP vertical display command VATosp SP 4415 137 LOG The display is scaled to the dB div specified by integers in the range 1 to 15 non integers are rounded Values outside this range cause the 494P to report an error LIN The display is scaled in volts div NUM is adjusted to the volts equivalent of the nearest 1 dB div If NUM is omitted the display is scaled to leave the reference level at its current value V D 1 8 volts equivalent of REFLVL INC or DEC changes the scale factor to the next step in the 1 2 5 volts div sequence if possible when FINE is OFF When FINE is ON the next step is determined by the 1 dB change in REFLVL that INC or DEC causes the new scale factor is 1 8 volts equivalent of REFLVL Power up value 10 dB division interaction The selection of 1 2 3 or 4 dB div with FINE ON causes the analyzer
138. nate delimiter to the block binary delimiter Line 540 Makes the 494P a talker and inputs the 494P WFMPRE and CURVE response until it reaches the percent sign storing the first seven numbers it finds as variables N X3 X2 etc These numbers are the waveform parameters sent in the WFMPRE query response Line 550 Dimensions the arrays to fit the incoming waveform Lines 560 580 Talk the 494P input the elements in the block binary format and untalk the 494P Lines 590 620 Scale the waveform integers and fill array M with the result The first number in each element of the array is a frequency the second number is the power detected at that frequency The elements can be printed on the screen with the statement PRINT M or any element can be printed with the statement PRINT M I Saving the Scaled Array A single statement WRITE transfers an array to tape First however you must find and mark an adequate tape file These statements do the job insert the number of the last tape file for N FIND N MARK 1 20000 FIND N WRITE 33 M These statements return the data from the tape FIND N READ 33 M Storing Settings If a particular series of settings are commonly used in an application it is recommended that these settings be stored within the 494P using the STORE command This practice will save program storage in the controller programming time and bus transfer time The settings can be recalled
139. nation The signai level at center screen point 500 must be at least 20 dB above the noise level A 10 MHz div span div will provide a good compromise between the time required to span down and the need to be 20 dB above the noise Send COUNT COUNT and input the signal fre quency The number returned will have a least significant digit of the current count resolution CRES command 100 PRINT Z SIG WAI FMA CEN 110 PRINT Z SIG WAI FMA POI FMIN POI 120 INPUT Z X Y X1 1 130 IF Y 1 lt 50 THEN 200 140 PRINT Z COUNT COUNT 150 INPUT Z F 200 REMARK Code to handle low signal level condition Using COUNT CF To go to a narrow span from a wide span without having to span down re center the signal etc use the CNTCF command Position the signal as indicated previously for COUNT check for 20 dB above the noise level and send CNTCF Now select the desired span div It is important to make sure sufficient count resolution CRES is selected for the desired span div The CRES selected should be less than 0 1 of the span div desired If many different span divs are being used it is more convenient to leave CRES set to 1 Hz 100 PRINT Z SIG WAI FMA CEN 110 PRINT Z SIG WAL FMA POI FMI POI 120 INPUT Z2 X X1 2 130 IF Y Y1 lt 50 THEN 200 140 PRINT Z CNTCF SPAN 3S 200 REMARK Code to handle low signal level condition Higher Center Frequency Drift Rate After Tuning A
140. nction front panel display data I O waveform processing and system operation Section 8 is a how to section for making programmable measurements with the 494P Appendix A will help you understand the GPIB and the IEEE 488 standard on which it is based Appendix B includes two foldout pages containing an in dex and a comprehensive list of remote control commands and queries and error event responses Document Standards and References Used Terminology used in this manual is in accordance with industry practice Abbreviations are in accordance with ANSI Y1 1 1972 with exceptions and additions explained in parentheses after the abbreviation Graphic symbology is based on ANSI Y32 2 1975 Logic symbology is based on ANSI Y32 14 1973 and the manufacturer s data books or sheets A copy of these ANSI standards may be obtained from the Institute of Electrical and Electronic Engineers 345 47th Street New York NY 10017 Change History Information Any unincorporated change information that involves manual corrections and or additional information is located behind the tabbed Change Information page at the back of this manual History information with the updated data is integrated within this manual when the page s is revised A revised page is identified by a revision date located in the lower inside corner of the page 494P Programmers TABLE OF CONTENTS Page Page Praa aaaea ie ada Ghote SAREE IES i Section 2 GETTING
141. nel Contro 494P Programmers FREQUENCY Figure 4 2 The commands in this group set and change the 494P center frequency FREQ and TUNE set the 1st LO FIRST and the 2nd LO SECOND frequencies disable frequency corrections DISCOR select the frequency range FRORNG turn the counter mode on and off COUNT se lect counter resolution CRES transfer signal count to cen ter frequency CNTCF and activate the A frequency function DELFR Degaussing current DEGAUS can be applied to restore preselector alignment Another command EXMXR selects the EXT MIXER input INTENSITY TE HOR OTA PLAY IEA STORAGE a 0 FREQUENCY py RESOLUTION DATA enay spawrony O aanowioT REFERENCE Levet S mwar artense POWER O a EES oun 4 QEZ ane ran apa Figure 4 2 Front panel Frequency Control commands 4 3 Front Panel Control 494P Programmers FREQ TUNE FREQ center frequency command CDHE 4415 90 NUM The analyzer centers its span about the value in the command argument If that frequency is not within the current band the analyzer selects the nearest band to the current band that encompasses the value The range of val ues and resolution of the instrument response are the same as for front panel operation Power up value 0 MHz Interaction An automatic degauss is done when FREQ
142. nly those devices se lected with PPC will accept PPD Appendix B 494P Programmers INTERFACE MESSAGES DCL 20 Clears I O buffer and status byte F GET 8 Aborts and then rearms sweep GTL a Go to focal contro IFC IFC line initializes talker and listener functions LLO 17 Lock Lockout PPC 5 Parallel poll configure i PPU 21 Parallel poll unconfigure SDC 4 Same as DCL if listener addressed SPD 25 Seriai poll disable SPE 24 Serial poll enable TCT 9 Take control STATUS BYTE 87654321 Decimal Condition 010X000 1 65 81 Power on o0ox0x0010 2 18 66 82 End of Sweep 000x0000 0 16 Ordinary operation ox1x0001 33 49 97 113 Command error i 0X1X00 10 34 50 98 114 Execution error ox1x0011 35 51 99 115 internal error 0X1X010 1 37 53 101 117 Execution error warning 0X1X0110 38 54 102 118 Internal error warning N me thes Four bit status code i 494P microcomputer busy condition Abnormal 1 normal 0 condition i SRQ is asserted depends on RQS and EOS commands Power on is reported only if an internal switch is set to request this status 9861 INF AIH WEP 09 S OL ZHW OO epnyidwe pue aun Aouenb 84 404 UORe OU Buyseulbue ul syun Aq pamoyioy eq Aew WON 430 0 NO 4 440 40 NO 10 paynpsqns eq Aew WAN uoye ou OYRUBIOS JO WUIOd Buyeo y veBequ UAaQWWMN UHP L Si WON huan
143. nnector specified for your product Use only a power cord that is in good condition Refer cord and connector changes to qualified service personnel For detailed information on power cords and connectors see the Maintenance section in the 494 494P Service manual Volume 1 494P Programmers Use the Proper Fuse To avoid fire hazard use only the fuse of correct type voltage rating and current rating as specified in the Re placeable Electrical Parts list in Volume 2 of the 494 494P Service manual for your product Refer fuse replacement to qualified service personnel Do Not Operate in Explosive Atmospheres To avoid explosion do not operate this product in an explosive atmosphere unless it has been specifically certi fied for such operation Do Not Remove Covers or Panels To avoid personal injury do not remove the product cov ers or panels Do not operate the product without the cov ers and panels properly installed ix 494P Programmers The TEKTRONIX 494P Programmable Spectrum Analyzer Section 1 494P Programmers INTRODUCTION TO GPIB OPERATION INTRODUCTION The TEKTRONIX 494P adds remote control and auto mated spectrum data acquisition and analysis to the perfor mance and portability features of the TEKTRONIX 494 Spectrum Analyzer The 494P front panel can be controlled remotely except for those controls intended for local use only such as INTENSITY Waveform processing funct
144. ower level of the CAL OUT signal s fundamental frequency The 494P microcomputer takes into account the MIN RF ATTEN dB and MIN NOISE settings when positioning the attenua tion and gain 2 1 Getting Started 494P Programmers The 494P powers up with the automatic modes active and in MAX SPAN to display all the frequencies You can restore this condition at any time with the INIT initialize command 4050 Series Controller How do steps 1 2 and 3 in the last example work on a Tektronix 4050 Series controller The 494P commands are inserted in the following GPIB output statement PRINT Throughout the 4050 Series BASIC exampies in this man ual the variable Z has been assigned to the value of the 494P GPIB address Any constant can be used to represent the number for the GPIB address 100 PRINT Z FREQ 100 MHZ 110 PRINT Z SPAN 1 MHZ 120 PRINT Z REFLVL 20 DBM or 100 PRINT Z FREQ 100 MHZ SPAN 1 MHZ REFLVL 20 DBM As this last statement shows all three commands can be strung together delimited by semicolons When the 494P executes these commands it tunes the CAL OUT signal to center screen magnifies the narrower span and changes the reference level to display the signal peak at the top of the screen Frequency range resolution bandwidth time division input attenuation and IF gain are changed automatically as necessary Because the 494P is calibrated for this display as part of the tur
145. pdates the FRQRNG query response before handshaking out array ele ment F 1 in line 130 Synchronizing with the Sweep Spectrum data can be acquired synchronously with the sweep that updates digital storage if a WAIT command is inserted in the message to the 494P Generally WAIT is placed immediately after a SIGSWP command that arms a sweep so that data is acquired from a full sweep WAIT delays the execution of commands or queries that follow in the same message until the fuil sweep is completed This means you can direct the 494P to acquire process and output data all in the same message If the commands or queries you add to process or output data follow WAIT the results will be based on data acquired by the SIGSWP com mand For example enter 100 DIM P 5 110 PRINT Z SIGSWP 120 FOR I 1 TO 5 130 PRINT Z FREQ 313 GHZ SIGSWP 140 PRINT Z WAIT FMAX POINT 150 INPUT Z P I 160 NEXT I Line 110 Sets the 494P to the single sweep mode if the 494P is not already in the single sweep mode Succeeding SIGSWP commands arm the sweep Lines 130 and 140 illustrate how to use WAIT WAIT follows SIGSWP and precedes the command and query that ready the 494P to output the updated data The 494P does not handshake out the data in line 150 until it finishes exe cuting the message in lines 130 and 140 This simple routine only gets the X variable of the display data point In this case it is the horizon
146. present If this occurs the controller is allowed to request updated spectrum data and be guaranteed that the data has been updated The request message would be similar to SIGSWP SIGSWP WAIT WFMPRE CURVE The first SIGSWP command sets the analyzer to the single sweep mode if it was previously in a repetitive sweep mode The next SIGSWP arms the sweep and WAIT suspends further execution until the sweep completes The message ends by the request of a waveform preamble and data The analyzer should be triggered or set to FRERUN lf the sweep is in the single sweep mode and is not armed the READY light is on when the microcomputer en counters WAIT the microcomputer continues to execute the message in the buffer and does not wait 2 WAIT is terminated if DCL or SDC while listener addressed is received This results in flushing the input and output buffer so any commands that follow WAIT are aborted See Status Byte later in this section 7 4 interaction WAIT delays execution of any portion of a message that follows until one of the termination conditions just outlined occurs There is no WAIT query REPEAT repeat execution command REPEAT SP NUM gt gt 4415 65 NUM This determines the number of times the micro computer is to repeat the execution of commands or queries that precede REPEAT NUM range 0 to 16 777 215 224 1 Since REPEAT may itself be one of the commands that precedes a
147. program run from the controller designates the primary talker and primary listener status of the desired instruments by coding data bits 6 and 7 1 0 respectively for a talker and 0 1 respectively for a listener Secondary talk and listen addresses or commands are represented by the controller sending both data bits 6 and 7 as a logical 1 The controller may listen to bus traffic without actually ad dressing itself over the bus SH and AH Source and Acceptor Handshake Functions NOTE Although discussed under one heading the SH and AH functions are independent of each other The SH Source Handshake function guarantees proper transmission of data while the AH Acceptor Handshake function guarantees proper reception of data The inter locked handshake sequence between these two functions guarantees asychronous transfer of each data byte The handshake sequence is performed via the NRFD DAV and NDAC signal lines on the bus see Figure A 5 Both func tions must respond to ATN within 200 ns The SH function must wait for the RFD Ready For Data message plus wait at least 2 us before asserting DAV This allows the data to settle on the data bus If three state driv ers are used the settling time is reduced to RFD plus 1 1 us Faster settling times are allowed under special conditions as noted in the standard The time it takes for the AH function to accept an interface message byte is dependent on how the designer impl
148. programming data A remote local interface function indicates to an instrument that the instrument will use either information input from the interface remote or to information input by the operator via the front panel controls local EOI End Or Identify A talker can use the EOI signal line to indicate the end of a data transfer sequence The talker asserts EOI as the last byte of data is transmitted In this case the EOI line is essentially a ninth data bit and must observe the same settling time as the data on the data bus When an instrument controller is listening it assumes that a data byte sent with EOI asserted is the last data byte in the complete message When the instrument controller is talk ing it may assert the EOI signal line as the last data byte is transferred The EOI line is also asserted with the ATN line true if the controller conducts a parallel polling sequence on the bus The EO line is not used for a serial polling se quence i i IEEE STD 488 GPIB System Concepts 494P Programmers INTERFACE FUNCTIONS AND MESSAGES introduction The ten major interface functions listed in Table A 1 pro vide a variety of capabilities and options for an instrumenta tion system These functions may be implemented in or for any particular instrument with instrument hardware or with a programming routine software Only those functions nec essary for an instrument s purpose need be implemented by the
149. r DT Controller c IEEE STO 488 GPIB System Concepts 494P Programmers NOTE The IEEE Std 488 standard defines the ten interface functions the specific protocol and timing relation ships by the use of state diagrams Not every instru ment on the bus will have all ten interface functions incorporated because only those functions important to a particular instrument s purpose need be implemented A TYPICAL GPIB SYSTEM A typical GPIB instrumentation system is illustrated in Figure A 2 and it includes the nomenclature for the sixteen active signal lines Only four instruments are shown con nected directly to the control bus but the GPIB can support up to fifteen instruments connected directly to the bus However more than fifteen devices can be interfaced to a single bus if they do not connect directly to the bus but are interfaced through a primary device Such a scheme can be used for programmable plug ins housed in a mainframe where the mainframe is addressed with a primary address code and the plug ins are addressed with a secondary ad dress code To maintain the electrical characteristics of the bus a device load should be connected for each two meters of cable length Although instruments are usually spaced no more than two meters apart they can be separated farther apart if the required number of device loads are lumped at any given point For proper operation at least two thirds of the instruments connected di
150. rac ter string for a a query and branch to input the response Instead the response is read after every message and printed a blank line if the 494P sends a byte with all ones The SRQ handler employs another 494P feature Rather than print a code for the status byte the routine asks for the error that caused the SRQ EVENT This offers much more specific information about the problem The meaning of the event codes is listed in Table 7 4 in Section 7 The routines assume you have assigned the value of the 494P address to variable Z or LZ TZ or z as previously discussed it is also assumed your input and output charac ter strings will fit P This gets further attention with regard to the instrument settings query SET our next topic In the routine for the CP1100 and CP4100 Series con trollers lines 10 and 20 are added to load the software driver and disable the bus timeout feature in this driver 4050 Series Controller 100 ON SRQ THEN 200 110 PRINT ENTER MESSAGE 120 INPUT P 130 PRINT 2 P 140 INPUT Z P 150 GO TO 110 200 POLL Q1 Q232 210 PRINT Z EVENT 220 INPUT Z P 230 PRINT P 240 PRINT SRO 3Q2 250 RETURN CP1100 and CP4100 Series Controllers 10 LOAD GPI 20 SIFTO N 1 100 WHEN N HAS SRQ GOSUB 200 110 PRINT ENTER MESSAGE 120 INPUT P 130 PUT P INTO N LZ 140 GET P FROM N TZ 150 PRINT P 160 GO TO 110 200 POLL N Q2 Q1 Q0 T2Z 210 PUT EVENT
151. ration 8 Section 2 494P Programmers GETTING STARTED INTRODUCTION Getting started with the 494P on the GPIB is a simple matter if you are already familiar with a GPIB controller If not talking to the 494P over the bus may be the easiest way to get over any uncertainty you feel about getting started The 494P speaks a friendly language that includes mne monics for control of the front panel and other parameters and to transfer measurement data Put these mnemonics into GPIB input output statements in your controller s lan guage and you re on your way Of course your controller must handle details such as asserting REN unaddressing bus devices and addressing the 494P to start communica tion but these are steps taken by most controllers when executing a GPIB 1 O statement We have included some sample programs and exercises adapted for the Tektronix 4050 Series controllers in BA SIC Tektronix CP1100 and CP4100 Series controllers in TEK SPS BASIC and the Hewlett Packard 9826A controller NOTE Some of the lines of input in examples of controller programs in this section extend beyond the column width limitations Where this occurs the overrun in formation is indented on the immediately following line mportant whenever a line is broken it is always where a natural space occurs So be sure to add a space when inputting the program SETTING AND QUERYING PROGRAMMABLE CONTROLS SETTING PROGRAMMA
152. rectly to the bus must be in the power on state IEEE STD 488 GPIB System Concepts 494P Programmers INSTRUMENT A ABLE TO CONTROL TALK amp LISTEN CONTROLLER DATA BUS 8 SIGNAL LINES INSTRUMENT B TALK AND LISTEN DIGITAL MULTIMETER TRANSFER BUS HANDSHAKE 3 SIGNAL LINES INSTRUMENT C LISTEN ONLY SIGNAL GENERATOR INTERFACE MANAGEMENT BUS ts 5 SIGNAL LINES INSTRUMENT D DIO1 DIO8 DATA INPUT OUTPUT LINES 8 TALK ONLY a COUNTER DAV DATA VALID F NRFD NOT READY FOR DATA NDAC NOT DATA ACCEPTED d IFC INTERFACE CLEAR ATN ATTENTION SRQ SERVICE REQUEST REN REMOTE ENABLE EO END OR IDENTIFY Figure A 2 A typical GPIB system A 4 IEEE STD 488 GPIB System Concepts 494P Programmers Table A 2 INTERFACE MESSAGES REFERRED TO IN THIS APPENDIX AND FUNCTIONS Mnemonic Message Interface Function Remote Messages Received ATN Attention AH C L LE PP SH T TE DAC Data Accepted SH DAV Data Valid AH DCLa Device Clear DC GET Group Execute Trigger DT GTLa Go To Local RL IFC interface Clear C L LE T TE LLO Local Lockout RL MSA My Secondary Address LE TE 4 MTA My Talk Address TTE PPCa Parallel Poll Configure PP PPDa Parallel Poli Disable PP PPE Paralleli Poll Enable PP v PPus Parallel Poli Unconfigure PP REN Remote Enable RL RFD Ready For Data SH p SDC Selecte
153. rface it holds up the handshake until the microcomputer can get involved The microcomputer will get involved as soon as it can service the interrupt The front panel ADDRESSED light and the crt readout will be modi filed as soon as the microcomputer can execute the programs that update the addressed status Because the microcomputer gets involved when a cur rent address is received addressed commands are im pacted by the speed at which the microcomputer can service interrupts Serial poll is similarly affected if MTA pre ceded SPE 3 GTL is handshaked immediately by the interface If the 494P is already listen addressed the microcomputer re turns the 494P to local contro executes GTL after execut ing any message in its buffer except WAIT or message units following WAIT REN unasserted is handled in the same manner as the GTL command 4 DCL requires microcomputer action that will hold up the handshake if the microcomputer is busy If the 494P is listen addressed the microcomputer treats SDC in the same manner These two device clear messages are exe cuted as soon as they are accepted 5 GET also requires action by the microcomputer so its handshake occurs only when the microcomputer can handle the interrupt GET is executed immediately aborting the current sweep and rearming the sweep 6 Parallel polls are handled by the microcomputer so PPC PPE PPD and PPU must wait for the microcomputer to service the interrup
154. rm and the B waveform which is continuously up dated The difference trace baseline is normally set at grati cule center but may be varied internally 4415 182 OFF The difference display is turned off NUM 1 equals ON numbers 0 5 are rounded to 1 Number 0 equals OFF numbers less than 0 5 are rounded to 0 Power up value Off Interaction BMINA ON turns SAVEA ON SAVEA OFF turns BMINA OFF BMINA B A waveform display query 4415 183 Response to BMINA query wH 4415 184 4 30 DSTORE store display command ae Cr oS The readout associated with the display is stored with the display 4415 185 A The A waveform is stored in the battery powered memory indicated by NUM range 0 8 B The B waveform is stored in the battery powered memory indicated by NUM range 0 8 There is no DSTORE query DRECAL recall display command EDO Ea Omn DRECAL ms NUM CD A A waveform from the memory specified by NUM 0 8 is recalled and put in the A waveform display 4415 186 B A waveform from the memory specified by NUM 0 8 is recalled and put in the B waveform display If BVIEW or BMINA is on the readout associated with a re called B waveform is displayed if AVIEW is on and BVIEW and BMINA are OFF the readout associated with a recalled B waveform is displayed In all other cases the current in strument readout is displayed There is no DRECAL query Inter
155. rm processing commands allow you to analyze signals without reading in ail the display data and operating on it in your controller Line 150 Inputs the analyzer response Line 160 Because the response to each query in line 140 begins with a mnemonic for the function the analyzer out put string acquired in line 150 is intelligible as is and the frequency and reference ievel readings are printed at the controller Line 170 Readies the analyzer to do it again Getting Started 494P Programmers Line 180 Goes around again The waveform processing commands and query allow you to analyze data without reading waveforms and manip ulating them in your controller More details can be found in Section 6 and instructions for putting 494P waveform pro cessing to work are given in Section 8 Section 3 494P Programmers DEVICE DEPENDENT MESSAGE STRUCTURE AND EXECUTION INTRODUCTION The goal of the 494P device dependent message struc ture is to enhance compatibility with a variety of GPIB sys tems yet be simple and obvious to use This goal is achieved within the framework of the Tektronix Interface Standard for GPIB Codes Formats Conventions and Features This standard is intended to make messages on the bus unambiguous while allowing the instrument to handle messages in a friendly manner i e to accept variations in the message Compatibility with ex isting devices is maintained as much as possib
156. ror An example is RESBW 10 KHZ in the max span mode The 494P sets the warning status because the UNCAL indicator is fit internal error warning This reports that a non fatal operating condition has been detected by the 494P micro computer Busy This is reported whenever the 494P micro computer executes a message in its input buffer This in cludes the WAIT command while waiting the microcomputer reports busy status Wace Neen Affect of Busy on Device Dependent Messages The microcomputer will not accept any further device dependent messages while the busy condition exists if made a listener it asserts NRFD Commands that require microcomputer interaction with the hardware can keep the microcomputer busy for a second or more significant to some bus controllers for instance commands such as DEGAUS and INIT The waveform processing commands and PEAK AUTO can also require significant processor time Of course long messages such as the SET response take a while to execute see Execution Times Table 8 1 in Section 8 Although output operations such as the CURVE response may take a long time to complete the microcomputer is busy only for the time it takes to load the output buffer Affect of Busy on Interface Messages Interface messages and the rt message from the RESET TO LOCAL button are processed despite busy status If RESET TO LOCAL interrupts the execution of a message the microcomput
157. s and adding a constant to approximate the positive noise peaks Adjust the constant if resolution bandwidth is changed Another method is to force signals off screen with the FREQ command and use FMAX to acquire the most positive noise peak In practice a combination of these methods may be ap plied to handle varying conditions For example smooth the data with the narrow video filter and average it as it is ac quired to enable the search routine to find signals close to the noise fioor Spectrum Search The RGTNXT and LFTNXT commands support spectrum search applications Begin with the display data point at the left edge of the screen POINT 1 Acquire a waveform with the SIGSWP command don t update digital storage with successive sweeps while the search is under way Let successive RGTNXT commands pick off the signals on the display To continue tune up in frequency by an amount equal to the span div multiplied by 10 take a single sweep and continue with RGTNXT 8 9 Helps and Hints 494P Programmers LFTNXT could be used by starting at the right of the screen POINT 1000 and tuning down in frequency rather than up A way to let the 494P loop through a message that uses RGTNXT to search for a spectrum is presented in connec tion with REPEAT later in this section Measuring Signal Frequency with COUNT To measure the frequency of a signal center the signal on screen This can be done by using a FMAX CENSIG combi
158. s a full 1000 point waveform as explained under Display Data Point Com mands Interaction later in this section Second NUM This is the Y value of a display data point The vertical scale is the same as illustrated for the CURVE query in Section 5 if the second number is omitted the microcomputer in terrogates digital storage for the value of the waveform at X the first number This makes the display data point corre spond to a point in digital storage If the second number is supplied in the POINT command the display data point may not correspond to any point in digital storage Example POINT 500 150 center screen PO 1 25 screen bottom left PO 1000 225 screen top right Power up value 500 225 6 1 Waveform Processing 494P Programmers POINT FIBIG LFTNXT RGTNXT Interaction The SET response sent back to the in strument sets both the X and Y values of the display data point which may not correspond to any point in digital stor age See Display Data Point Commands Interaction POINT display data point query Pont 4415 27 Response to POINT query Cont On j 4415 28 The first number is the X value of the display data point the second number is the Y value of the display data point Note that the query response may not match any point in digital storage if the Y value was set by a POINT command or if digital storage was updated after the display data point was a
159. s execute a hand shake sequence via signal lines DAV NRFD and NDAC see Figure A 5 the ATN line is shown to illustrate the controller s role in the process DAV Data Valid The DAV signal line is asserted by the talker after the talker places a data byte on the data bus When asserted low DAV tells each assigned listener that a new data byte is on the bus The talker is inhibited from asserting DAV as long as any listener holds the NRFD sig nal line asserted NRFD Not Ready For Data An asserted NRFD signal line indicates one or more of the assigned listeners are not ready to receive the next data byte from the talker When ail of the assigned listeners for a particular data byte transfer have released NRFD the NRFD line becomes unasserted high When NRFD goes high the RFD message Ready For Data telis the talker it may place the next data byte on the data bus A IEEE STD 488 GPIB System Concepts 494P Programmers PRIMARY nr SECONDARY LISTEN ADDRESS ADDRESS ATN ASSERTED ASSERTED ASSERTED CONTROLLER INSTRUMENTS Figure A 4 An example of data byte traffic on the GPIB ATN CONTROLLER DAV TALKER NRFD LISTENER NDAC LISTENER l 1 H Leg BYTE CAPTURE TIMES DATA l BUS LAST INTERFACE MSG ee FIRST DATA BYTE FROM TALKER FROM CONTROLLER DEVICE DEPENDENT MSG Figure A 5 A typical handshake timing sequence idealized Byte capture time is dependent
160. s response does not follow the standard 4 35 Front Panel Control 494P Programmers PTYPE POFSET PTYPE plotter type command POFSET set K command a FOES A em Le nr ee eet 4415 205 NUM Sets K in the B A K formula for plotting B A waveforms using PLOT NUM is limited to the 0 to 255 range and sets K to the nearest limit if out of range no error reported 4415 202 TK4662 The TEKTRONIX 4662 is selected as the plotter to be driven by the data generated by PLOT POFSET set K query TKOP31 The TEKTRONIX 4662 Opt 31 is selected as GO the plotter to be driven by the data generated by PLOT 4415 206 s q HA HP7470 The Hewlett Packard HP7470A is selected Response to POFSET query as the plotter to be driven by the data generated by PLOT os the rear panel LF OR EO switch must be in the LF OR EOI i position up mj NUM 0 equals TK4662 1 equals TKOP31 and num 4415 207 bers 2 equal HP7470A W Nee PTYPE plotter type query 4415 203 Response to PTYPE query aa Sow 4414 204 4 36 2 Section 5 494p Programmers DISPLAY DATA AND CRT READOUT 1 O INTRODUCTION The commands and queries refer to Table 5 1 in this section transfer display and readout data to or from the 494P Additional information on waveform transfer and storage is available in Section 8 NOTE Some of the lines of input in examples of
161. selected the current spectrum data being acquired in B memory can be compared to the wave form saved in A memory Putting a Counter on the Tape How do you keep track of where you are on the tape You can keep track of files going by when you use the 4924 Forward and Reverse buttons Or you can record a mes sage on every other tape file as a marker With the latter scheme press Forward and then Talk after either recording or playing back a file This causes a message with the num ber of the next file to appear on the 494P crt Here s a 4050 Series program to mark and record the tape for this purpose 100 REMARK PROGRAM TO MARK TALK LISTEN TAPE 110 FOR I 1 TON 120 FIND 2 I 1 130 MARK 1 500 140 FIND 2 I 1 150 PRINT 33 RDOUT FILE NEXT PRESS FORWARD RDOUT 160 FIND 2 I 170 MARK 1 4500 180 NEXT I me cee S This program works on a tape that has been previously marked for any purpose For a new tape enter the following 4050 Series commands before running the program FIND 1 MARK 1 500 Line 110 Substitute the number of files you want to mark for N Line 150 The RDOUT command replaces the crt readout with a message showing the file count and a reminder to move to the beginning of the file Line 170 Each time through the loop the file is marked to be used for recording As an alternative the PRINT statement in line 150 could be expanded to include an instrument setup To do this make up a charac
162. sent a func tion for example FREQ for center frequency and CURVE for the display trace Header Delimiter SP A space SP must separate the header from any argument s Argument Delimiter A comma must separate multiple arguments Argument Format The following diagram illustrates that arguments follow ing the header may be numbers groups of characters or either linked to a character argument al UNITS pe FORMAT CHARACTER CHARACTER as ARGUMENT UNITS CHARACTER ARGUMENT FORMAT CHARACTER CHARACTER _ ARGUMENT 4415 52 Numbers The defined element NUM is a decimat number in any of three formats NR1 NR2 or NR3 NR is an integer no decimal point 4415 53 REV FEB 1984 NR2 is a floating point number decimal point required 4415 54 NR3 is a floating point number in scientific notation DIGIT nnr 4415 55 NUM arguments may serve two functions The first is to select the value of a continuous function for example the center frequency via FREQ In this case if NUM exceeds the range of the function the 494P microcomputer does not execute the command but issues an error message see PEAK and POINT in Sections 4 and 6 respectively for ex ceptions Numbers within the range are rounded The sec ond function of a NUM argument is to substitute for character arguments in ON OFF or mode selection In this
163. set up to enable the operator to adjust the front panel AMPL CAL control CAL AMPL has an indeterminate execution time and will operate until either a device clear DCL is received via the GPIB port or the 494P is returned to local control via the instrument front panel An instruction message appears on the screen CAL HPOS The instrument is set up to enable the Operator to adjust the front panel horizontal POSITION con trol Horizontal POSITION has an indeterminate execution time and will operate until either a device clear DCL is received via the GPIB port or the 494P is returned to local control via the instrument front panel An instruction mes sage appears on the screen 4 18 CAL VPOS The instrument is set up to enable the operator to adjust the front panel vertical POSITION con trol Vertical POSITION has an indeterminate execution time and will operate until either a device clear DCL is received via the GPIB port or the 494P is returned to loca control via the instrument front panel An instruction mes sage appears on the screen Power up value Off Interaction Due to the internal procedures required to perform CAL CAL AUTO CAL LOG and CAL AMPL an error message ERR 52 or ERR 54 will be delivered upon completion of these operations To eliminate the message input the following program RQS 0 CAL ERR RQS 1 CAL cal query CAL 4415 144 Response to CAL query Coan Ld Ot O O
164. ssing The results of waveform processing depend to a great extent on the data in digital storage Both the resolution and noise factors mentioned previously can be controlled during data acquisition Signal resolution can be improved by selecting a nar rower resolution bandwidth RESBW command You may need to slow the sweep so the data is calibrated done auto matically in the TIME AUTO mode Noise can be overcome in several ways To reduce noise peaks smooth the data by averaging in digital storage Av eraging is enabled by the CRSOR command use CRSOR AVG or CRSOR KNOB setting the cursor above the noise by turning the front panei knob Further smoothing is possi ble by slowing the sweep TIME command so that the num ber of data averaged for each point in digital storage is increased Noise peaks can also be reduced smoothed by the video filters The narrow video filter VDFLT NARROW is recommended for acquiring data for most waveform pro cessing applications There is an alternative to smoothing the data The signal search commands can include a parameter that sets a threshold for the signal search routine If this parameter is set above the noise but below any desired signal the rou tine ignores the noise and finds the signal But how do you find this level that is not too high and not too low There is no one level that will work in every case A level may be estimated by using FMIN to locate the negative noise peak
165. tal location of the point with the largest value in digital storage The Y variable is lost each time through the loop when the 494P receives further input before it can handshake out the second POINT argument Figure 8 1 further illustrates the two program concept one in the controller and one in the 494P and how they are synchronized with the sweep for data acquisition This fig ure charts the execution of the two programs arrows be tween the programs relate how one waits for the other The WAIT command is executed in the loop that tests for the end of sweep this synchronizes data acquisition with the sweep 8 2 Using the End of Sweep SRQ Although the previous method for synchronizing controlier 494P execution with the sweep is recommended there is another method This alternative may be necessary for some operating systems or application programs that allow a short response time when the 494P is made a talker or that must take care of other tasks while the 494P is ac quiring data In such cases the controller can enable the 494P end of sweep SRQ to synchronize data acquisition with the sweep The following example just shifts the WAIT from the 494P program to the 4050 Series BASIC program to exercise the SRQ It could be modified however to busy the controller with some other task using the SRQ subrou tine to test the status byte and perform input when end of sweep status is detected i 100 DIM P 5
166. talked Remem ber if you change these switches after the 494P is already powered up you must press RESET TO LOCAL or lt SHIFT gt PLOT to cause the microcomputer to update the primary address Setting the LF OR EO Switch Switch 3 of the rear panel GPIB ADDRESS switch see Figure 1 3 selects the terminator for messages on the bus If LF OR EO is selected switch up 1 the 494P interprets either the data byte LF or the end message EOI asserted concurrently with a data byte as the end of a message If EOI is selected switch down 0 the 494P interprets the byte sent with the end message EO asserted as the end of a message This switch also selects the output terminator Set to LF OR EOI the 494P adds CR and LF with EOI asserted con currently after the last byte of the message Set to EOI the 494P asserts EO concurrently with the last byte of the message Figure 1 4 shows the effect of this switch for both input and output Select EOI switch down for Tektronix controllers The other position of this switch is provided to accommodate some other controllers such as the Hewlett Packard 9826A A change in this switch takes immediate effect 1 3 Introduction to GPIB Operation 494P Programmers TALK ONLY LISTEN ONLY Switches The 494P switches for talk only and listen only operation are part of the GPIB ADDRESS switch bank shown in Fig ure 1 3 Set either or both switches an extension of the IEEE 488 standard
167. ter Message units are separated by the ASCII code for semi colon A semicolon is optional following the last message unit Message Terminator TERM The end of message terminator may be either the END message EOI asserted concurrently with the fast data byte or the ASCII code for line feed LF sent as the last data byte The active terminator is selected by the rear panel GPIB ADDRESS switch 3 Format Characters Format characters may be inserted at many points to make the message more intelligible but are required only if they are included as a literal element i e in circles or ovals with no bypass Allowable format characters are space SP carriage return CR and line feed LF as well as all other ASCII control characters and comma At some points in a message the 494P may accept other non alphanumeric characters 3 2 Input Buffering and Execution The 494P buffers each message it receives with a capac ity that exceeds that required for the SET response The 494P waits until the end of the message to decode and execute it A command error in any part of a message pre vents its execution When the instrument is under local con trol commands that would conflict with local contro are ignored see Remote Local under IEEE 488 Functions in Section 1 If the message contains multiple message units none are acted on until the 494P sees the end of message termina tor When the 494P sees the term
168. ter string to hold both the control settings and a crt message When the analyzer receives this longer string it will restore its controls to make the desired mea surement and display a message to the operator Introduction to GPIB Operation 494P Programmers IEEE 488 FUNCTIONS The 494P is compatible with IEEE Standards 488 1975 and 488 1978 The connector and the signal levels at the connector follow the specifications in the IEEE 488 stan dards Table 1 2 lists 494P interface capabilities as defined in the standards Table 1 2 494P IEEE 488 INTERFACE FUNCTIONS Function Implemented As Source handshake SH1 Acceptor handshake AH1 Talker T5 Listener L3 Service request SR1 Remote local RL1 Parallel poll PPI Device clear DC1 Device trigger DT1 Controller co Source Handshake SH1 The 494P has complete capability for transfer of mes sages to other devices on the bus Although tri state drivers are used on the data lines T1 DAV delay for data setting is greater than 2 us Acceptor Handshake AH1 The 494P has complete capability to receive messages on the bus Talker T5 The 494P employs the complete talker function including serial poll unaddresses as a talker when addressed as a listener The analyzer operates in a simple system in a talk only mode if the TALK ONLY switch is set to 1 Listener L3 The 494P employs the complete listener function unad dresses as a listener when
169. than the selected location To avoid this use only a one pen one color configuration or manually select the second color pen to be used Follow these steps to make a two color piot 4 Switch GRAT ILLUM on and turn the crt READOUT and Digital Storage off REV FEB 1984 2 Manually select a pen and plot the information 3 Turn off the GRATicule ILLUMination and turn on the crt READOUT and Digital Storage 4 Manually select the second color pen and plot the stored display and crt readout Version 2 2 Auto Peaking Function with External Mixers When using external mixers the automatic peaking func tion does not always succeed in setting the correct peak value To be sure of having the correct value set peaking manually with the front panel PEAK AVERAGE control or use the PEAK command with specific numeric arguments 8 13 Helps and Hints 494P Programmers EXECUTION AND TRANSFER TIMES The 494P microcomputer system typically takes 10 to 25 ms to execute commands received over the bus This is the time the 494P is busy following receipt of the end of message terminator EOI or LF depending on the switch Execution time for some commands stretches beyond 25 ms however because of interaction between the micro computer and hardware or a wait to allow hardware re sponse These cases are noted in Table 8 1 Table 8 1 EXECUTION TIMES Table 8 1 cont Command Time Command Time FREQ IDENT ON A 0 1 8 G
170. that the alphanumeric codes associated with the numbers symbols and upper case characters decimal 32 to 94 in the ASCII Code Chart Fig ure A 3 be used to compose device dependent messages One example of a device dependent message could be the following ASCH character string MODE V VOLTS 2 5E 3 FREQ 1 0E3 The ASCH character string sent with the ATN line unasserted tells the instrument to set its front panel con trols to the voltage mode and output a 2 5 mV signal at a frequency of 1000 Hz When 8 bit binary codes other than the iSO 7 bit are used for device dependent messages the most significant bit should be on data line Di08 for bit 8 To summarize the difference between interface control messages and device dependent messages on the data bus remember that any message sent or received when the ATN line is asserted low is an interface control message Any message data bytes sent or received when the ATN line is unasserted high is a device dependent message GPIB SIGNAL LINE DEFINITIONS Figure A 2 shows how the sixteen active signal lines on the GPIB are functionally divided into three component buses an eight line data bus a three line data byte transfer control handshake bus and a five line general interface management bus The data bus contains eight bi directional signal lines DI01 through D108 information in the form of data bytes is transferred over this bus A handshake timing sequence be tween
171. the analyzer displays signals within its bandpass RESBW about its center frequency FREQ An execution error mes sage appears on the screen if the number is too small or too large INC The next larger span division is selected in the front panel 1 2 5 sequence if possible If the analyzer de faults to MAX SPAN an execution error message appears on the screen DEC The next smaller span division is selected in the front panel 1 2 5 sequence if possible If the analyzer de faults to zero span an execution error message appears on the screen MAX The entire frequency range is swept Power up value MAX SPAN frequency span division query 4415 120 Response to SPAN query mH 4415 121 Front Panel Control 494P Programmers SPAN ZEROSP ZEROSP zero span mode command ZEROS 4415 122 ON The 494P is converted to a continuous tune mode with the frequency sweep defeated The crt readout shifts to the TIME DIV mode on the horizontal axis instead of FREQ SPAN DIV ON saves the previous FREQ SPAN DIV which is restored when ZEROSP is turned OFF OFF ZEROSP ON is cancelled leaving the FREQ SPAN DIV at the previously selected value NUM 1 equals ON numbers gt 0 5 are rounded to 1 Number 0 equals OFF numbers less than 0 5 are rounded to 0 Power up value Off Interaction When the SPAN setting is changed ZEROSP is turned off ZEROSP zero span mode query 44
172. the Memory board Table 7 3 TEST CONVERSION Version 670 8431 00 Chart Circuit Circuit Device Location Board Number ROM 0 A54 Memory U2015 1 A56 GPIB U1012 2 A56 GPIB U1018 3 A56 GPIB U1022 4 A56 GPIB U10243 5 A56 GPIB u2013 6 A56 GPIB U2018 7 A56 GPIB u20229 8 A54 Memory U1021 9 A54 Memory U1014 RAM 1 A54 Memory U1032 2 A54 Memory U1027 3 A54 Memory U2014 4 A54 Memory U2021 5 A54 Memory U2044 6 A54 Memory U2039 7 A54 Memory U2032 ROM 4 was U2013 in version 670 7896 00 gt ROM 5 was U2018 in version 670 7896 00 e ROM 6 was U2022 in version 670 7896 00 d ROM 7 was not installed in version 670 7896 00 System Commands and Queries 494P Programmers Error and Event Codes re 00 INSTALLED OK Q1 INSTALLED BAD 10 NOT INSTALLED NON VOLATILE VOLATILE 4415 17A Figure 7 1 TEST Conversion Chart 7 10 REV FEB 1984 Error and Event Codes The Tektronix Interface Standard for GPIB Codes Formats Conventions and Features specifies device dependent Error and Event codes by category Table 7 4 System Commands and Queries 494P Programmers Error and Event Codes identifies each general category and lists the codes within that category Following the listing are the specific error messages returned by the 494P Error codes are returned in numerical order as they appear in the table When the cur rent code s is read the error response is cleared
173. the controller to squeeze out unneeded spaces be tween the numbers as the PRINT statement transmits array A Without a semicolon immediately after the array variable this line does not run properly in some 4050 Series control lers With this semicolon the controller places a space be tween numbers the 494P accepts the space or other format characters as well as a comma for a delimiter WAVEFORM PROCESSING ASCH OR BINARY WAVEFORM INPUT WAVEFORM OUTPUT BLOCK BINARY p L 1 WFMPRE ENCDG b a 3401 157 Figure 8 3 How multiple use of the display data buffer is controlled Helps and Hints 494P Programmers FINDING SIGNALS WITH 494P WAVEFORM PROCESSING The waveform processing resident in the 494P packs a lot of power into a portable analyzer This power can be better realized if you understand how the routines work and what their limitations are This portion of the manual will try to help you gain that understanding and suggest how to apply 494P waveform processing in your application with more accurate and predictable results Understanding How Waveform Processing Works The signal finding commands FIBIG LFTNXT and RGTNXT are programmed to recognize a shape in the stored waveform that is characteristic of a continuous wave cw signal This means complex signals such as those cre ated by frequency modulation may be overlooked depend ing on their relative amplitude and spac
174. the first line is discarded and the new RDOUT command characters become the 16th line Use single quote marks instead of double quote marks to delimit RDOUT messages in 4050 Series BASIC statements Reserve double quote marks to enclose the en tire message sent by the PRINT statement as 100 PRINT Z RDOUT SET CONTROLS AS DESIRED NORMAL Normal 494P readout is restored Example RDOUT TEKTRONIX 494P RDO SET CONTROLS AS DESIRED RDOUT NOR Power up values Normal readout Interaction If a crt message sent with a RDOUT com mand remains on the screen after the analyzer is returned to local control normal readout can be restored by changing any control that causes the normal readout to be updated REDOUT ON is required to see any crt readout The TEXT command switches between 2 line and 16 line modes There is no RDOUT query TEXT change readout mode command SHORT DH 7 LONG SHORT The GPIB accessible readout is switched to the 2 line mode with a spectral display RDOUT commands will load characters to these two lines 4415 44 LONG The GPIB accessible readout is switched to the 16 line mode without a spectral display RDOUT com mands will load to the top line first then to successive lines until all are filled When all 16 lines are filled the entire screen scrolls up TEXT LONG will clear the page of read out and initiate entry of characters into the top lin
175. to enter a A amplitude mode See FINE for a discussion of this mode VRTDSP vertical display query Cams 4445 138 Response to VRTDSP query LOG Je nat vaTDsP 9 un oC of nas 4415 139 4 16 PA iunt REFLYL reference level command oe cole NUM REFUL 6P a a Cc ___ be oe 4416 140 NUM The analyzer sets the reference level to the nearest dBm step for a log vertical display except in the A A mode and to the nearest dBm step for a linear vertical dis play The argument to the REFLVL command is always an absolute reference level and not an offset to the present reference level though the crt readout shows relative amplitude INC or DEC The reference level is stepped up or down once The step value is determined by the value of the VRTDSP scale factor and FINE selection refer to Table 4 3 Table 4 3 REFERENCE LEVEL SETTINGS Step Size VERTDSP Scale Factor FINE ON FINE OFF 15 dB 1 dB Equal to VRTDSP scale factor 14 dB 1 dB Equal to VRTDSP scale factor 13 dB 1dB Equal to VRTDSP scale factor 12 dB 1dB Equal to VRTDSP scale factor 11 dB 1 dB Equal to VRTDSP scale factor 10 dB 1 dB Equal to VRTDSP scale factor 9 dB 1 dB Equal to VRTDSP scale factor 8 dB 1 dB Equal to VRTDSP scale factor 7 0B 1 dB Equal to VRTDSP scale factor 6 dB 1 dB Equal to VRTDSP scale factor 5 dB 1 dB Equal to VRTDSP scale factor 4 dB A A mode Equal to VRTDSP scale
176. ts before they can be executed This assumes that the 494P was addressed for the parallel poll sequence Busy and end of sweep are independent Busy exists only while the microcomputer is executing a command and end of sweep indicates that sweep and data updating are complete If a single sweep command is sent the micro computer remains busy only until it can initiate the sweep while end of sweep does not occur until the operation is complete When polled the 494P reports a status code related to its SRQ if any Bit 5 always reflects the current condition A serial poll clears the status byte that is reported Since sta tus is stacked a new SRQ may be sent immediately 7 7 System Commands and Queries 494P Programmers DT EVENT ALLEV NUMEV EVOQTY DT device trigger enable command 4415 72 ON GET is enabled to trigger a new sweep OFF The response to GET is disabled NUM 1 equals ON numbers 0 5 are rounded to 1 0 equals OFF numbers less than 0 5 are rounded to 0 Power up value On DT device trigger enable query 4415 73 Response to DT query eet 4415 74 EVENT event information query EmO 4415 75 The EVENT query returns more detailed information about the event that was reported in the last serial poll sta tus byte It also allows a controller to get information about events when the controlier s RQS assertion capability has been disabled by RQS OFF Response to EV
177. ts contain ASCII characters except when a binary waveform is requested Output Message Format The output message unit combines the header and ap propriate argument s Message units are combined if the output includes a response to the SET query or to more than one query a he 4415 57 3 4 Output Message Execution The analyzer begins output when talked and it continues until it reaches the end of the information in its buffer or is interrupted by a device clear DCL untalk UNT or inter face clear IFC message If the analyzer is interrupted and the buffer is not cleared the analyzer will resume output if it is retalked The buffer may be cleared by the DCL message or if it is listened by the SDC message or any device dependent message If not interrupted the analyzer termi nates the output according to the setting of the EO OR LF switch Device Dependent Message Structure and Execution 494P Programmers 494P 492P COMPATIBILITY Most of the primary modes of the 494P controls and functions are identical to those of the 492P Following are some of the areas where operations or results will differ GPIB 494P The DCL interface message is handled by inter rupts and will stop execution of the command in progress 492P The processor is required to not be busy e g executing a WAIT message in order for DCL to be handshook in DEGAUS Command 494P DEGAUS may be executed in any sp
178. tton on the analyzer to transmit the instrument settings and waveform The mes sage is formatted so that when it is played back to the ana lyzer it restores the settings and display The message is a combination of the responses to the SET and CURVE queries If SAVEA is OFF A and B are transmitted as a full waveform A and B memories merged for 1000 points SET RESPONSE OH CURVE RESPONSE e FULL 4000 POINTS 4415 88 If SAVEA is ON A and B are transmitted as separate waveforms 500 points each SET CURVE CURVE RESPONSE 3 RESPONSE eE Sno A 500 POINTS B 500 POINTS 4415 89 1 5 introduction to GPIB Operation 494P Programmers The analyzer transmits waveform data as ASCll coded decimal numbers unless changed to binary by the ENCDG argument in a WFMPRE command You ll find the full CURVE response syntax diagram in Section 5 See Sec tion 7 for the full SET response syntax diagram NOTE if an internal switch is changed the analyzer reports control settings only when RESET TO LOCAL is pressed Refer questions about setting this internal Switch to qualified service personnel The 4924 keeps listening or talking if Talk is pressed until the message transfer is completed there is no reset switch except Power Once the 494P starts talking it keeps talking until it is finished and cannot be interrupted except by turning off the power This is true only if the
179. ue pa1a55u 203p 10 oep cc kejdsip 2103s 34OLSG cep ce Aejdsip e982 FwOSYHa eg oct aqueesd ejdsip gaudd gp ouenn suoy081100 a1gesIp HOOSIG ero teeseeeers Kguanbey v Y47130 gep ouenn 09 Buun ssne p snY93A ego kedsip Adoo LAdOOG roo terssi aano ejdsip SAND iet i serere osn eBesene yeed YOSHI seeeeveeeeeeeses UORNOS 40409 SIHO Aasai 4a un09 INNOD Kouenbey 184U39 0 JUNOD JOLNO eeeee ees euyjaseg dijo di19 ve ceeaeeeeeeneeese YORBIgHES TWO po reese eee beta tee peisant yeuBis 139 u39 DISNSO Aeydsip wuojenem a MIJAS Reidsip uuojanem y 8 WNING Aeydsip wuoyenem y MIIAY uipympued uoynjoses ome S3YY g coc OTAS ANTEE te s uaaa jie A3 TIY oed yun ebessow SNOILdINOSAd AHANO GNV ANYWWOO XIGNAddV dr6t SIAUWELIOId dbsp a xipueddy dams jo pua eyajduu0o uonesrwdQ 86 uo eweoysnfuemog 46 sjuaag wejshs pauinooo yeas peziuBooaun 66 payoojes eoueiajes Aouenbes4 06 uoyeinSes poureBas Aiddns wamog 68 anje e Wo4 paiaao0a1 UNOD J BB aunwwey e Woy pasonooes Wayshs YOO SeUd 8 empe e WOJ Pa1 Acde wass Buum Oq puz v8 asnje e woa pesoncoas Was S Sulun 071S Z8 p yoojun eoueiajes Aouanbesj 08 uoneinGei yo yno jddns samod 6L pape unos 3 BZ popes wayshs yoo eseUd SZ pape was s Buun OT UZ p4 pae wayshs Buun 073S ZZ aona wnsyoayo WH paamod Aoneg Z9 aunye uopeaqaeo 49 07 454 40 Buryoojun uo enez Buyejuecay 09
180. uency function is turned on As the fre quency is changed the crt frequency readout indicates rela tive frequency rather than absolute frequency Only the readout operates differently FREQ and FREQ response still refer to absolute frequency The resolution of the read out will be the lesser of the current readout resolution and the readout resolution when the DELFR mode was turned on OFF The A frequency function is turned off NUM 1 equals ON numbers 0 5 are rounded to 1 Number 0 equals OFF numbers iess than 0 5 are rounded to 0 Power up value Off DELFR A frequency query Cm O 4415 113 Response to DELFR query o 4415 114 4 8 DEGAUS degauss tuning coils command aa 4415 115 A degaussing current is turned on to remove residual magnetism in the ist LO and preselector tuning coils This improves preselector tracking amplitude accuracy when the preselector is not PEAK d at each frequency This function is performed automatically by the 494P when FRQRNG is changed and when CENTER FREQUENCY is changed by more than 1 GHz There is no DEGAUS query Se Front Panel Control 494P Programmers EXMXR EXMXR external mixer input command 4415 116 ON The front pane EXT MIXER input is selected which requires an external mixer OFF The coax RF INPUT is selected NUM 1 equals ON numbers 0 5 are rounded to 1 Number 0 equals OFF numbers less than 0 5
181. use of the display buffer that is using the buffer for more than one purpose during execution of a message Also at several points in this manual you are informed of possible interaction involving waveform pro cessing and waveform data O executed in the same 494P message This occurs in Section 5 under the Interaction part of the CURVE command and under Display Data Point Commands Interaction in Section 6 There is no conflict in many cases because the 494P buffers the message you send and then executes it in the order you sent it For exampie you can use the 494P as a waveform pro cessor for spectrum data you previously acquired in array A by entering 100 REMARK BUFFER DEMO 110 PRINT Z CURVE 3A FIBIG POINT 120 INPUT Z B1 B2 in this case the 494P does what you ask it loads a waveform into digital storage and returns the point at the peak of the largest signal Interaction is possible in other cases however because there is only one display data buffer used for both display input and output and as workspace for waveform process ing For instance conflicts can arise when more than one of these message units is executed in the same message CURVE CURVE POINT if Y argument omitted FIBIG LFTNXT RGTNXT FMAX FMIN Whether interaction results in invalid data depends on the relative position of these message units in the message This follows from how these message units use the buffer Buffer
182. uz GNOOSS wuojanem y Aes VAAVS serete goes ysenbe SOH epow jane 89u948484 SAOWTY eubis yxou 146y puy LXNLOY uypimpueg uopnjosa MaSSY uognoexe yeade IWaday jeae 890328421 TAIS3SY Aeidsip nopeaa LNOGSY s6um s peo TIVOSY gt eBessew ynopee LNOGY serete gdAy seyoid AdALd a Quod eyep Aeidsip LNIOd 4 388 13S40d ayoqegs esind HLSTd sereset eyep 301d ELOTd terene Gupjead yyad syuane Jo sequunu AJWNN pun eBessow Chi eS i pow ueds xew NdSXW er i poy unwixew IHX z uonenueye gy wnwiuu LIYNIW zev srereeeeees Mod Mdu unwxew YMdXYN eg oeenn nopea amol 008407 pg oecon s yeubis x u 49 puy LXNIST ex oc r1 s6um s zyenui LINI pep occ he ee SHEE IA Ajnuap LNAGI eg ounn span e eee e renee Quewnaysu Aynuep al pepo au puewwoo 10 1x8 diay pues 2d 73H eer 1 yoneuruuny aNoNe6 LWHD oF ue Aouanbexy ONYOYA rr pereresseeess Kouanbouy 40 U80 OSHS eo seve cere eeeee eee eeeee sess anea wnNuwtu puy NINA eg ccc enjen wnwxew puy XV ep ooe resete Kou nb s 07 384 LSHIS erp ooe sereesees gdays jong 300918431 Buy INIA bg ciotccrcierretitereres s feubis ysa66ig putj Dials ep cots Qndu saxi euseyxe YXWXS gee hne raien Ayquenb uaaa ZALOAS BL creer uoneuuoju uaaa LN3A3 ep REP ee end pe ree deems jo pua S03 E ajqe
183. whenever needed with the RECALL command Waveform Plotting A simple routine plots array W the integers output by the 494P The plot see Figure 8 2 is embellished by labels de rived from the waveform preamble obtained by the previous program 700 REMARK SIMPLE WAVEFORM PLOT 710 VIEWPORT 10 110 10 90 720 WINDOW 1 N 1 250 730 PAGE 740 AXIS N 10 25 N 2 75 750 MOVE 1 W 1 760 FOR I 2 TON 770 DRAW 1 W 1 780 NEXT I 790 MOVE N 2 5 800 PRINT X1 HZ 810 MOVE N 75 820 PRINT Y1 Y2 75 Y3 DBM 8 5 Helps and Hints 494P Programmers 1 0E 9 Hz 4415 39 Figure 8 2 A simple plot of a spectrum acquired from the 494P Line 710 Shrinks the plot slightly to leave room for labels Line 720 Sizes the plot for the data Line 740 Marks off cross hairs as a reference for the plot Add more AXIS statements if you wish to mark the reference level or fill in other parts of the graticule Lines 750 780 Draw the plot point by point Lines 790 and 800 Label the X axis center marked by the vertical cross hair with the center frequency 8 6 Lines 810 and 820 Label the amplitude marked by the horizontal cross hair six divisions below the reference level The vertical cross hair extends over the full 10 divisions of vertical data including a full division above and below what you see on the 494P crt If there is data in digital storage from these areas outside the 494P display the data is ac quire
184. x GRAT Lighted graticule Dark graticule Off CLIP Blank trace at bottom of crt Full trace Off NUM 1 equals ON numbers gt 0 5 are rounded to 1 0 equals OFF numbers less than 0 5 are rounded to 0 Display control query imemonic 4415 194 Response to display control query Con MNEMONIC SP T OFF 4415 195 4 33 Front Panel Control 494P Programmers HELP GENERAL PURPOSE Figure 4 8 The general purpose commands and queries request the RECALL plot crt information PLOT on a choice of plot command list or front panei help messages HELP store ters PTYPE and plot the B A K formula POFSET settings in memory STORE recall settings from memory Tektronix 4g4P eE en smer ges N asl vo a ma O Pa Leon Fremricat POEG DOTAT DISPLAY AER STORAGE FREQUENCY gy RESOLUTION SPAN OWy O eanownorn REFERENCE LEVEL MIN AF ATTEN 0B wk r meat serena ne Sree as oe f ano eg ee Ret Lae sie Treo Figure 4 8 Front panel General Purpose commands and queries HELP send help list of command list query The response includes a list of all command headers in the 494P GPIB language Response to HELP FPANEL query 4415 196 eo ana Response to HELP query with no argument 4415 198 Each string represents one crt readout
185. y the B waveform is filled with data from the current sweep so half resolution transfers can in volve two unrelated waveforms 5 2 WFID Either the A or B waveform or both A and B FULL waveforms are selected for data transfers and wave form processing ENCDG Either ASCil coded decimal numbers or bi nary numbers are selected for data transfer The two arguments may be selected independently or strung together in the same command Example WFMPRE WFID FULL WFMPRE ENCDG ASC WFM WFID A ENC B Power up value Full 1000 point ASCll coded digits WFMPRE waveform preamble query oe wrMPne 4415 36 Response to WFMPRE query NAS HOG O riii e ee BY a Senne OO O O O OAD O AS 4415 37 items that follow the waveform identification and coding specify other data packet parameters that refer to number of points scaling and error checking NR PT Specifies either 500 or 1000 points in the curve to follow PT FMT Y Indicates all curve data is Y display verti cal values The data is ordered each point s X display hori zontal value is determined by its point number and parameters in the waveform preamble PT OFF Relates the first point to the X origin by the point offset XINCR Is the difference between adjacent data points XZERO Points to the X origin
186. you insert into the statement and may finish by sending UNL and UNT If the controller does not assert REN automatically for GPIB I O you can set it with an earlier control statement The 494P does not balk if REN is not set except if you send commands that change front panel settings or data in digital storage That leaves the most important part up to you what goes in the controller statement as a device dependent message The 494P control mnemonics are collected for quick reference on a Program Summary foldout chart at the back of this manual For details on how to state each com mand correctly and the instrument response turn to the command descriptions that begin in Section 4 The detailed descriptions are arranged by function the front panel func tions are in Section 4 with other functions covered in follow ing sections refer to the Index for page numbers The 494P executes the message when it sees the mes sage terminator either EOI or LF Message syntax and command execution is given fuller treatment in Section 3 Getting Started 494P Programmers 4415 86 QUERYING PROGRAMMABLE CONTROLS The 494P returns the state of programmable controls when queried This takes two steps 1 Query the 494P The query takes the form of the mne monic for a function name followed by a question mark 2 Read the response A GPIB input statement does the job in the case of most controllers For example the auto resolution mode

Tektronix 494P User's Manual

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