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1. Data store half full Reading done Ready Error Enable EOI and bus hold off on X Disable EOI enable bus hold off on X Enable EOI disable bus hold off on X Disable both EOI and bus hold off on X CR LF 3 9 15 LF CR CR Send machine status word Send error conditions Send translator word Send buffer size Send average reading in buffer Send lowest reading in buffer Send highest reading in buffer Send current value Send input switch status front rear2. Sted 5d 5rd 5Std 6d 5d 5 d 5 d 6 d RER6 5 d 5 d 62d 30 kQ 30 kQ hms 5 2d 5 2d R7 Integration period 3 d 318psec 4 2d 2 59msec 5 d and 6 2d Line cycl Continuous on Talk One shot on Talk Continuous on GET One shot on GET Continuous on X One shot on X Continuous on External Trigger One shot on External Trigger 3 15 IEEE 488 PROGRAMMING Reading Mode Data Store Size Data Store Interval Value Calibration Default Conditions Data Format EOI and Bus Hold off Multiplex Table 3 8 Device Dependent Command Summary Cont BO Readings from A D converter B1 Readings from data store lee E Continuous data store mode Data store of n n 1 to 500 One shot into buffer 3 9 9 n interval in milliseconds Imsec to 999999msec Calibration value zero value 3 9 10 V n nnnnnnE CO Calibrate first point using value V 3 9 10 Ci Calibrate second point using value V LO Restore factory default conditions and save L1 3 9 11 L1 Save present machine states as default conditions G0 Reading with prefixes 3 9 12 G1 Reading without prefixes G2 Buffer readings with prefixes and buffer locations G3 Buffer readings without prefixes and with buffer locations G4 Buffer readings with prefixes and without buffer locations G5 ATA readings without prefixes and without buffer ocations Disable Reading overflow Data store full
3. opens and initializes a device descriptor that opens commu nication between the IEEE Controller and the DMM You will be prompted for the board or Controller index 0 the primary and secondary addresses of the DMM 7 and 0 and other information that you will find in Chapter 6 of the User Manual If you like you can enter all of this information following the ibdev command instead of waiting to be prompted 2 Type ibclr and watch the Keithly 196 as you do so Note and explain the changes you see in your lab book This command sends the IEEE SDC command see above to the DMM It also sends a LLO local lockout command notice that the function buttons on the DMM no longer respond 3 Type ibloc which returns command to the instrument by sending a GTL go to local command Watch what happens to DMM panel lights and note that DMM function buttons respond again 4 Type ibclr again and then use ibrd and ibwrt to send commands to the DMM and read data from it A description of these commands is given in the Ref erence Manual See if you can strip away the alphabetic descriptors in the DMM output change the meter function and so on using ibwrt Again watch the DMM panel lights and be sure you understand why they are changing 5 When you are finished type ibonl 0 to take the DMM off line Interface or Board Level Mode This mode is more complex but gives considerably more detailed control over the IEEE Controlle
4. IEEE DATA ACQUISITION REFERENCES National NI 488 2 User and Reference Manuals These manuals come with the National Instruments IEEE 488 interface board for the lab PC that we will use in this experiment Various instrument manuals for example the Keithley Model 196 DMM Instruc tion Manual Various Basic and Visual Basic Manuals NOTE Manuals may be checked out from your instructor They are not to be taken out of the Science Hall and you are PERSONALLY RESPONSIBLE for letting your instructor know where the manuals are and for returning them after the experiment I Introduction Very often the actual taking of experimental data can be a tedious and time consuming part of an otherwise interesting experiment Thus one important function of the computer for scientists and engineers is to automate data acquisition and it is the function of this experiment to introduce you to that process There are a number of methods of interfacing computers to experiments the one that you will study here uses the IEEE 488 standard somtimes also referred to as gpib for gen eral purpose interface bus or hpip for Hewlett Packard interface bus It has the following advantages and disadvantages Advantages of the IEEE 488 interface 1 It is easy to use The electronics are already built into the instruments such as voltmeters frequency counters oscilloscopes etc so that one does not have to do much electronics before starting an ex
5. UNL UnListen 7 UNT UnTalk These last two commands place all devices in the IDLE state for example UNL disables all current listeners A WwW N e IV DEVICE SPECIFIC COMMANDS In addition to the standard IEEE 488 commands listed above each device manu facturer will usually define a set of commandes that are specific to each instrument For example the Keithley manual for the Model 196 Digitial Multimeter that you will use in this experiment has a set of commands that relate to the operation of the meter These commands are usually sent as messages that is they are sent with the ATN line unasserted You will find list of these commands at the end of this section of the write up Similarly the NI 488 2 controller card and software used on the lab PC has numerous device specific commands that implement the IEEE standard They are discussed below but see the manuals for a full discussion V The Experiment NOTE You should write a detailed description of the actual procedure you follow in your laboratory notebook This description should be written while you are in the lab doing the experiment Do NOT rely on your memory or on rough notes taken on scrap paper Do NOT simply copy the suggested procedure in this writeup write down what you actually do The experiment consists of three parts 1 Play with the computer and the IEEE 488 apparatus and learn how they work using the Interactive Control utility Here th
6. ard that plugs into a slot inside the computer That board serves as the CONTROLLER that is it manages the bus sends commands to and receives data from the other devices on the bus and so on The board manufacturer National Instruments supplies a series of assembly language subroutines with the board so that the user can access the IEEE functions by calling those subroutines from a language like C BASIC or FORTRAN There is also an Interactive Control utility that you can use to become familiar with these commands A standard IEEE 488 cable to be described below connects the computer to the in struments Instruments can be connected in a chain that is one cable runs from the computer to the first instrument a second cable runs from the first instrument to the second and so on Up to 15 instruments can be operated from one IEEE board Each instrument is identified by an individual address a number from 0 to 30 that allows that instrument to be identified This address is the primary address in addition instrument manufacturers have the option of defining secondary addresses to assist with specific instrument functions The primary address is often set using a small DIP switch that is typically set on the back of or inside the computer In newer instruments the address can often be set using the front panel controls III TIEEE 488 cable and IEEE 488 standard commands The IEEE 488 cable consists of 24 lines These lines a
7. e only apparatus you will need is the computer an IEEE 488 device for example the Model 196 DMM and a power supply 2 Write a short Visual Basic program that takes control of the Model 196 DMM sets the mode and makes a measurement 3 Finally do the Newton s Law of Cooling experiment 1 Interactive Control Untility Begin by reading through Chapter 6 of the User Manual Then make sure the IEEE cable is connected to the Keithly Model 196 DMM digital multimeter and to the computer and turn on the power to the DMM Then find the National Instrument Measurement and Automation icon and double click to open MAX the Measurement and Automation Explorer Take a few minutes to look over the information given on screen which should include the IEEE addresses of both the DMM and the IEEE card in the computer Right Click on the instrument choose communicate with the instrument and make sure everything is working Then right click on the GPIBO and choose Interactive Control A command shell will open Go back to the MAX program and in the same way open the NI Spy untility this program will monitor the IEEE commands and let you know if there are any errors You can use the Interactive Control Utility in three modes Device Mode This mode is the easiest to use and the one you will probably want to use for you Visual Basic program later Proceed as follows 1 At the Prompt type ibdev This command
8. ervice ReQuest 5 EOI End Or Identify In addition there are a number of standard IEEE 488 commands that are sent on the data lines for these commands to be sent ATN must be asserted The names and functions of these commands are listed and sometimes briefly described below See the manuals for more information A Universal Commands go to all devices on the bus 1 DCL Device Clear Sets all devices on the bus to their default power up states those states are defined by the device manufacturer LLO Local LockOut Deactivates the front panel controls of all devices on the bus 3 PPU Parallel Poll Unconfigure 4 SPE Serial Poll Enable 5 SPD Serial Poll Disable B Addressed or Primary Commands go to specific device addresses 1 GET Group Execute Trigger Triggers a group of devices simultaneously SDC Selected Device Clear Similar to DCL but acts only on a specifically addressed device GTL Go To Local Returns control to the instrument s front panel controls 4 PPC Parallel Poll Configure 5 TCT Take ConTrol Used to specify another device as a controller used only if there exists a second device that can function of a controller C Secondary Commands PPE Parallel Poll Enable PPD Parallel Poll Disable MSA My Secondary Address MLA My Listen Address defines the controller as listener 5 MTA My Talk Address defines the controller as talker 6
9. llowing functions 1 Set the digital multimeter DMM to REN and LLO 2 Set the DMM to a non default state 3 Take an instrument reading 4 Remember that the instrument reading is initially in the form of a string Convert that string to a real number using the VAL command and perform some arithmetic operation on it for example add 5 to it Be sure that you save your work frequently When you have a working program demonstrate it for your instructor Be sure to print a copy to include in your lab notebook At this point you are ready to do an actual experiment and to see automated data acquisition in practice The experiment will involve Newton s Law of Cooling and is described in more detail below It will take some hours to take the data but you won t have to be there Once you set up the apparatus and start the program the computer will take the data IEEE 488 PROGRAMMING Table 3 8 Device Dependent Command Summary DC volts AC volts Ohms DC current AC current ACV dB ACA dB Offset Compensated ACV dB ACA dB Ohms Auto Auto Auto Auto 300mV 300mV 300 A 300 pA 3 V 3V 3mA 3mA 30MQ Auto Auto MQ Auto Auto Zero disabled Zero enabled Zero enabled using a zero value Filter disabled Filter on with a value of n n 1 to 99 5d Offset Compensa DCV ACV DCA ACA OHMS ACV dB ACA dB 0 3d 3d 3 d 3 d 3d RI R4 5 d 5 d R5 R7 4d 4d 4hd 4 d 4 d RER4 S d 54d 5d 5 d R5 R7 5d 5d 5 d 5 d
10. on for example a voltage reading to the controller NOTE Information is sent in the form of a string that is a series of ASCII characters If the string represents a number say a voltage the program must convert this string to a real number Let us see how this process works in more detail We begin by describing the five interface management lines Like most computer electronics these lines transfer digital information by switching between a low state typically 0 volts and a high state typically 5 volts Thus one speaks of a line being high or low asserted or not asserted or some similar terminology The names and functions of the five interface management lines are listed and sometimes briefly described below see the manuals for more complete descriptions NOTE It is often more effective to understand these commands by seeing how they are used than by puzzling too long over the definitions The long lists of commands can be a little intimidating when you see them for the first time but you will soon learn which ones are important for your application and how to use them 1 ATN ATtentioN When ATN is asserted information on the bus is interpreted as commands otherwise as messages for example meter readings 2 IFC InterFace Clear 3 REN Remote ENable When REN is asserted the instrument can be programmed by the controller that is from the computer in most cases 4 SRQ S
11. periment 2 It uses a reasonably standard set of commands 3 In most implementations high level programming languages such as C BA SIC and FORTRAN can to be used to program the experiment so that little or no assembly level programming is needed 4 Instruments that support the IEEE 488 interface are widely available Disadvantages of the IEEE 488 interface 1 In practice it is comparatively slow Although in principle the IEEE 488 stan dard supports data transfer rates of up to 1 MBytes sec in practice rates are generally much slower since few instruments are designed to support such fast transfer rates and those few are generally very expensive The instruments in the physics department are not particularly fast according to the manu als they can transfer instrument readings at rates up to several hundred per second We have rarely used them at rates faster than a few per second 2 The total cable length should not exceed 20 meters unless special and expen sive repeaters are used 3 Instruments equipped with IEEE 488 interfaces can be expensive 4 For some experiments standard instruments with an IEEE interface aren t available Thus for experiments that use standard instruments and for which comparatively slow rates of data transfer are adequate the IEEE 488 interface is a convenient and powerful way of automating an experiment II Physical Setup The IEEE 488 standard is implemented by a bo
12. r and the DMM Proceed as follows Set up the board by typing the following commands which you should look up in the Reference manual ibfind gpib0 Initializes IEEE interface see Reference Manual ibpad 0 ibrsc 1 ibsic ibsre 1 This command sets the index for the IEEE Controller to zero It may not be necessary but can t hurt anything requests system control for the IEEE board See Manuals Sends an IFC interface clear command Sends REN remote enable command Then use the following commands to communicate with the DMM ibcmd string Sends an IEEE command The string should be in quotes ibrd ibwrt For example x20 x47 sets the IEEE board at address 0 to LISTEN and the DMM at adddress 7 to TALK mode The x indicates a hexidecimal number See Appendix A in the Reference Manual for other examples See for example if you can set the Controller to listen and the DMM to talk These commands should work as before if the correct commands have been set using ibcmd As before use ibonl 0 to take the interface off line when you are finished Feel free of course to try some of the other commands discussed in the manuals Try iblines for example Multi Device Mode This mode is particularly convenient if you are using multiple IEEE devices but can be used even if you are using only one Initialize by typing set 488 2 0 at the Interactive Control prompt and see the manuals for command
13. re used as follows 1 There are eight ground lines 2 There are three control or handshake lines that are used to coordinate data transfer between the the controller and the instruments 3 There are eight bi directional data transfer lines that are used to send com mands back and forth between the instruments and the controller and also to transfer data meter readings and the like 4 Finally there are five general interface management lines The last two sets of lines are used to send commands back and forth between the instruments and the controller Each device must be designated as a TALKER a LISTENER or as IDLE At any one time there can be only one talker but there can be several listeners And at different times a given device can serve as both talker and listener Thus the controller is a talker when it sends instructions to a device and a listener when it receives data For example a typical data transfer might proceed as follows 1 The controller board on the PC is identified as a TALKER 2 The instrument for example a voltmeter is identified as a LISTENER NOTE Some inexpensive instruments are TALKERS only they cannot be set to a LISTEN mode 3 The controller sends commands to the instrument for example it can tell a Digital Multimeter to set itself to an ohmmeter mode 4 Next the controller tells itself to be the LISTENER and the instrument the TALKER 5 The instrument sends informati
14. s to try 2 Short Basic Program Once you understand the use of these subroutines in the Interactive Control utility the next step is to write a short BASIC program that uses them We will use Microsoft Visual Basic It has the disadvantage of being restricted to Windows as oppposed to Linux or UNIX but has the advantage of making it easy to write simple programs The first step if you have not done much programming is to learn something about BASIC programming in general and Visual Basic in particular Your instructor should have a few books or manuals you can use in getting started Proceed as follows 1 Start Visual Basic 2 Drag a Command Button to the Visual Basic form that will appear on screen 3 Double click the Command Button to open a code window here you can enter a short program that will execute when you click the command button while the program is running Don t be concerned if you haven t done a great deal of programming In this experi ment you will only need to write a short program There are both sample programs and faculty help available Once you can write a short program that does some simple arithmetic and reports the results you can proceed to write a program that will control the IEEE interface and the DMM There are sample programs that will help you get started Be sure to include comments in your program explaining what each section does Your program should perform the fo
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