Remote GPIB Control Using a GPIB-232CT-A
Contents
1. S11 095 S12 050 S18 000 S25 005 S26 001 S36 007 S37 000 S38 020 S44 003 S46 002 S48 007 S49 008 S50 016 STORED PROFILE 1 B1 B16 El L2 M1 N1 P QO V1 WOX4 YO amp C1 amp DO amp G0 amp JO amp K3 amp Q5 amp RO amp SO amp T4 amp X0 S00 000 S02 043 S06 002 S07 050 S08 002 S09 006 S10 014 S11 095 S12 050 S18 000 S25 005 S26 001 S36 007 S37 000 S38 020 S44 003 S46 002 S48 007 S49 008 S50 016 With the modem AT commands the S registers can be set using the Terminal program in the Accessories program group found in Windows 3 1 or any other application program that can communicate with a computer s serial port Once these modem settings have been set and saved on the modem the use of a computer with the remote modem is no longer necessary The following is a summary of AT commands used to setup the remote modem AT S0 1 Set modem to auto answer after ring AT S0 2 Set modem to auto answer after 2 ring AT S0 3 Set modem to auto answer after 3 ring AT amp V View Configuration Profiles Active and Stored AT amp WO Store the Active Profile into Stored Profile 0 AT amp W1 Store the Active Profile into Stored Profile 1 AT amp YO Select Stored Profile 0 on power up AT amp Y1 Select Stored Profile 1 on power up Using the GPIB 232CT A in S Mode To implement a remote GPIB control application the GPIB 232CT A can be configured to operate in S Mode In this mode the GPIB 232CT A functions as a GPIB system controlle2. a nonzero value to enable auto answering The default setting for the SO register is zero which disables auto answering The SO register must be set to SO 1 SO 2 or S0 3 for the modem to auto answer after one two or three rings respectively When the SO register is changed the changes are made to the active profile which contains the settings that the modem uses during operation The active profile is loaded from nonvolatile memory when the unit is powered up Therefore when changes are made to the active profile it is essential to save those changes to memory This memory is called stored profiles and for the Hayes 2400 modem these profiles are called stored profile 0 and stored profile 1 It is equally important to make sure that the correct stored profile is loaded when the unit is powered up This ensures that the remote modem will power up as an auto answering modem The following is an example of the active and stored profiles ACTIVE PROFILE B1 B16 El L1 M1 N1 QOT VO WO X4 YO amp C1 amp DO amp G0 amp JO amp K3 amp Q5 amp RO amp SO amp T4 amp X0 amp YO S00 002 S01 000 S02 043 S03 013 S04 010 S05 008 S06 002 S07 050 S08 002 S09 006 S10 014 11 095 S12 050 S18 000 S25 005 S26 001 S36 007 S37 000 S38 020 S44 003 S46 002 S48 007 S49 008 S50 016 STORED PROFILE 0 B1 B16 E1 L1 M1 N1 QOT V1 WO X4 YO amp C1 amp DO amp G0 amp JO amp K3 amp Q5 amp RO amp SO amp T4 amp X0 900 002 S02 043 S06 002 S07 050 S08 002 S09 006 S10 014
3. ComError M END MAIN 7 7 ae eA he he Ae 2 2 he Ae 2 2 he he Ae oe he 6 28 2 2 Ae 2 2 ee 6 2 he 6 2A 2 2 he 2S 2 oe A Function CheckCOMportError Parameters int error value returned Return Value NONE Description This function checks the com port ah error code and returns the appropriate message Error codes are referenced in LWCVI user manual 7 7 ae ae A he he he 2 2 he Ae 2 oe he he A oe he 26 28 2 2 Ae 2 2 2 he Ae A void CheckCOMportError int err_value if err_value lt 0 MessagePopup Communications Error Com Port Error Program Aborted exit 0 E E ae kk he k ak ak ak k ak ak ak ak a ak he ak 3k 3k 2 ak ak 2 3K 3K 3K akk ee 3K 3K 2 he 3K 3K 2 he he ak oe he he 3K Kak ie SK 2 K KK Function ReadAllStatus Parameters NONE wh Return Value NONE Description This function reads all status information returned by wait 78 7 ae eh he he he 2 2 oe 8 2 2 he he Ae oe he 6 28 2 2 he He 2 ee he A void ReadAllStatus void FillBytes Status 0 10 0 FillBytes GPIBerr 0 5 0 FillBytes SPerr 0 5 0 FillBytes count 0 5 0 BytesRead ComRdTerm 2 Status 10 13 BytesRead ComRdTerm 2 GPIBerr 5 13 BytesRead ComRdTerm 2 SPerr 5 13 BytesRead ComRdTerm 2 count 5 13 7 7 E k k k he k ak ak ak k ak ak ak he a ak he ak ak ak 2 ak 3k ak ak 3k 3K 2 3k he 3K 3K 2 he 3K 3K 2 he he ak 3K he
4. NATIONAL Application Note 059 INSTRUMENTS The Sotware i Gye nr Remote GPIB Control Using a GPIB 232CT A Amar Patel Chris LeBlanc William Lockett Introduction With the National Instruments GPIB 232CT A any computer with an RS 232 serial port can be a GPIB Talker Listener Controller For standard local operations the serial port of the GPIB 232CT A is connected to the serial port of the computer However if a pair of modems were inserted between the serial port of the computer and the serial port of the GPIB 232CT A existing modem communication technology could be used to achieve remote GPIB control Figure 1 shows the block diagram of such a system Phone Lire Sommunication Link S s hiodem hio de m AF IB 2325 T A FIB Figure 1 Typical Block Diagram of Remote GPIB Control with GPIB 232CT A An example of such an application is controlling a field test site from an office located in a city The test site is a remote station at which a spectrum analyzer is used to make measurements at a certain time each day Rather than having to travel to the remote station each day modems and the GPIB 232CT A could be used to interface an application program located on a computer in the office with the spectrum analyzer in the field The advantage of using a GPIB 232CT A is that a second computer is not needed at the field site and if several test sites were developed this could prove to be cost effective Modem Connections The firs
5. ad data from COM2 Buffer Disconnecting from Remote GPIB Controller Once data collection from the remote GPIB system has been completed the GPIB Controller should be taken off line BytesWritten ComWrt 2 onl O r 6 Place the GPIB 232CT A off line CheckGPIBError Send the escape sequence to place the local modem into Command Mode Then send the hang up command string BytesWritten ComWrt 2 3 Place local modem in Command Mode Delay 2 BytesWritten ComWrt 2 ATH r n 5 Hang Up To complete your application program close access to the computer serial port ComError CloseCom 2 CheckCOMportError ComError General Programming Considerations Delays are used from time to time to slow down portions of the code in order to allow ample time for information to be processed through the serial port You will need to experiment to determine where these delays might be necessary In addition flushing input and output queues prior to sending and receiving data checking the input queue prior to reading data from the serial port and checking for GPIB and serial port errors is highly recommended Error checking is important However an even more basic requirement is to clearly understand the syntax involved in using the S Mode functions For example whenever a command is sent to the GPIB 232CT A a specific type of termination character Generally a linefeed or a carriage return must be append
6. ed to the end of that command This allows the GPIB 232CT A to terminate correctly and recognize that a command has been sent to it and so in general be very careful to adhere to the syntax rules outlined for each S Mode programming function The LabWindows CVI example appearing in Appendix A illustrates the use of these termination characters when using the S Mode programming functions to interface with the GPIB 232CT A Many users may choose to use programming languages other than LabWindows CVI In general the entire interfacing process is streamlined somewhat if the user chooses a language that has standardized functions for easy access to your serial port QuickBasic HP Basic Visual Basic and the LabWindows programming environments have this particular feature Otherwise the user must access the UART that manages the computer serial ports on a register level in order to read write and check input and output queue lengths for a particular serial port To assist in porting the LabWindows CVI program in Appendix A to another language Appendix B describes the functions performed APPENDIX A LabWindows CVI Example Program include lt formatio h gt include lt gpib h gt include lt userint h gt include lt ansi_c h gt include lt utility h gt include lt rs232 h gt void CheckCOMportError int void ReadAllStatus void void CheckGPIBError void static int ComError static int Bytes Written static int BytesRead
7. he 3K Kak ie SK 2 K KK Function CheckGPIBError i Parameters NONE Wh Return Value NONE eh Description This function reads all status information returned by stat If an error condition exists display error code and exit prgm E E k k he he k ak ak a a ak ak ak he Ae a he ak ak 2 2 ake 3k 2 oe 3K 3K 2 ee 6 3K 2 he 26 3K 2 he he 2 oe he he 3K 2 he ie 3K 2 K ee void CheckGPIBError void Delay 2 FlushInQ 2 BytesWritten ComWrt 2 stat n r 7 while InQLen lt 4 InQLen GetInQLen 2 ReadAllStatus Scan Status s gt d amp hexStat Scan GPIBerr s gt d amp GPIBErrCode if hexStat lt 0 printf GPIB Error GPIB error code d n GPIBErrCode exit 0 10 APPENDIX B Description of the LabWindows CVI Functions Used in Appendix A Each of the RS 232 functions used in the LabWindows CVI program in Appendix A is described This information outlines the tasks accomplished by each function so that users can translate LabWindows CVI calls to other programming languages OpenComConfig This function opens access to a COM port in the desired configuration Parameters include the COM port number and its mnemonic baud rate parity data bits and stop bits as well as the ability to specify the size of software buffers that function as input and output queues for transmitting and receiving data It returns an error code that can be found in the LabWindo
8. ination and no EOS byte Each line of code that executes GPIB operations is followed by the function CheckGPIBError It is important to verify that no GPIB errors have occurred after executing a GPIB operation See the Application code in Appendix A for a listing of this function Bytes Written ComWrt 2 onl 1 r 6 Write six byte string to COM2 CT A Online CheckGPIBError Bytes Written ComWrt 2 sic r 4 Write four byte string to COM2 Send IFC CheckGPIBError The following code illustrates how to query a device on the GPIB for its identification The IDN string is used to prompt a IEEE 488 2 instrument to send its identification string on the next read from that device The device resides at address 8 BytesWritten ComWrt 2 wrt 8 n IDN r n 13 Query device for identification CheckGPIBError Device resides at address 8 BytesWritten ComWrt 2 rd 70 8 r n 10 Read back identification from device BytesRead ComRdTerm 2 databuf 100 13 Read identification from COM2 Buffer CheckGPIBError The following code illustrates how to conduct a serial poll by manually polling every device on the bus In this case the device at address 8 asserts SRQ when data becomes available The program returns status information using the ReadAllStatus function when SRQ is detected All status information is converted from ASCII to Hex and a Mask is used to check if the SRQI bit of GPIB sta
9. nce of the NI 488 2 driver software The functions are designed to be sent directly to the GPIB 232CT A via a serial link eliminating the additional overhead of the NI 488 2 software Establishing Communications with Your Remote GPIB Controller The following section outlines the steps required to establish a communications link with a remote test site interface with the GPIB 232CT A and then terminate the communications link with the remote test site once all GPIB activities have been completed The following subsections sequentially illustrate each step in the interfacing process using LabWindows CVI A complete listing of the source code appears in Appendix A Opening Serial Port Communications The following example code opens access to serial port 2 The serial port is configured to operate at 2400 baud no parity eight data bits one stop bit and an input output queue size of 512 bytes The communication mode is also set up for Hardware Handshaking CTS CheckCOMportError uses the variable ComError to check for serial port error conditions ComError OpenComConfig 2 COM2 2400 0 8 1 512 512 CheckCOMportError ComError ComError SetCTSMode 2 1 Require Clear To Send signal for handshaking data CheckCOMportError ComError Connecting to the Remote Modem The following example code illustrates how to configure a local modem via the serial port Once the configuration has been sent the next programming instruction e
10. r performing the various tasks required in managing a GPIB network of instruments These tasks include addressing Talkers and Listeners on the bus managing information transfer across the bus and managing requests for service by various devices on the GPIB The S Mode was designed into the GPIB 232CT A so users could remotely control GPIB instruments using the computer serial port Now we are adding modems and telecommunications links to remove the 50 ft distance limit of the RS 232 standard The following table summarizes all of the S Mode programming functions that can be used to control the GPIB 232CT A Similar to the NI 488 2 software routines and functions the S Mode programming set provides functions for I O High Level Bus Management Low Level Bus Management GPIB Initialization Serial Polling Parallel Polling and Serial Port Management For a more detailed discussion of each of the functions listed below consult the GPIB 232CT A User Manual Table 1 GPIB 232CT A Functions in S Mode Become Active Controller caddr address Change the IEEE 488 address of the GPIB 232CT A clr address list Clear specified device s id Mdenttify system ist set clear Set or clear individual status bit for use in GPIB 232CT A response to Parallel Polls Determine state of GPIB control lines Change serial port XON XOFF protocol The advantage of using S Mode programming to control the GPIB 232CT A is that these functions do not require the prese
11. sic r 4 CheckGPIBError BytesWritten ComWrt 2 wrt 8 n IDN r n 13 CheckGPIBError BytesWritten ComWrt 2 rd 70 8 r n 10 BytesRead ComRdTerm 2 databuf 100 13 CheckGPIBError printf s n databuf BytesWritten ComWrt 2 wrt 8 n SRE 16 r n 15 CheckGPIBError BytesWritten ComWrt 2 wrt 8 nVAL1 r n 13 CheckGPIBError Delay 2 FlushInQ 2 InQLen 0 BytesWritten ComWrt 2 wait 4096 r 10 while InQLen lt 4 InQLen GetInQLen 2 ReadAllStatusQ Scan Status s gt d amp hexStat if hexStat amp 0x1000 Delay 2 FlushInQ 2 FillBytes spoll 0 5 0 hexSpoll 0 BytesWritten ComWrt 2 rsp 8 r 6 BytesRead ComRdTerm 2 spoll 5 13 Scan spoll s gt d amp hexSpoll if hexSpoll amp 0x40 BytesWritten ComWrt 2 rd 70 8 r n 10 BytesRead ComRdTerm 2 DCbuf 70 13 Delay 2 FlushInQ 2 FillBytes spoll 0 5 0 hexSpoll 0 BytesWritten ComWrt 2 rsp 2 r 6 BytesRead ComRdTerm 2 spoll 5 13 Scan spoll s gt d amp hexSpoll if hexSpoll amp 0x40 BytesWritten ComWrt 2 rd 70 2 r n 9 BytesRead ComRdTerm 2 DCbuf 70 13 BytesWritten ComWrt 2 onl O r 6 CheckGPIBError FlushOutQ 2 BytesWritten ComWrt 2 3 Delay 2 BytesWritten ComWrt 2 ATH r n 5 Delay 3 ComError CloseCom 2 CheckCOMportError
12. stablishes a communications link with the remote site by dialing the remote modem Each modem is different so you must determine the correct configuration string for the modem that you are using BytesWritten ComWrt 2 ATQOV1E1S0 0 r n 14 Send Configuration String Delay 2 BytesWritten ComWrt 2 ATDT97945775 r n 14 Dial Remote Modem Once the connection has been established the local modem returns a connection response string in the serial port input buffer We use this string to verify that the connection has been made in the desired configuration The modem itself is automatically placed into Data Transfer Mode by writing directly to the serial port you can send information over the modem link to your remote GPIB 232CT A while InQLen lt 4 Wait for Response String InQLen GetInQLen 2 Check input queue for data BytesRead ComRd 2 databuf 80 Read Response String if strncmp databuf r nCONNECT 2400 14 0 Check for Valid Connection printf Connection Succesful n else printf No Carrier Connect Unsuccessful n exit 0 Remote Interfacing with the GPIB 232CT A The following code illustrates how to initialize the GPIB 232CT A as System Controller Users can also use the tmo eot and eos functions to modify time out termination method and the end of string features respectively The code below assumes the default settings of 10 second time out EOI term
13. static int Flag static int handle static int hexStat static int hexSpoll static int nQLen static int GPIBErrCode char Status 10 char GPIBerr 5 char SPerr 5 charcount 5 char databuf 100 char DCbuf 100 char Timeout 5 char spoll 5 main eR REE REE EE OPEN amp CONFIGURE COM2 HW HANDSHAKE ComError OpenComConfig 2 COM2 2400 0 8 1 512 512 CheckCOMportError ComError ComError SetCTSMode 2 1 CheckCOMportError ComError BytesWritten ComWrt 2 ATQOVIE1S0 0 r n 14 Delay 2 Bytes Written ComWrt 2 ATDT97945775 r n 14 Delay 2 FlushInQ 2 InQLen 0 while InQLen lt 14 InQLen GetInQLen 2 BytesRead ComRd 2 databuf 80 if strncmp databuf r nCONNECT 2400 14 0 printf Connection Succesful n else printf No Carrier Connect Unsuccessful n exit 0 Delay 2 FlushInQ 2 Command IDN returns instrument ID from 488 2 Instrument 1 Command SRE 16 enables the Service Request Enable register of a 488 2 instrument Instrument will assert SRQ ef when data ready Command VAL 1 instructs our device to return DC voltage Wh E E E eA he he k ak ak ak k k ak ak ak af ak ak ak 2 2 ake 3k 2 akk 6 6 2 afk he Ae 2 2 he AS 2 2 he he 2 2 he 3K 3K 2 he 3K 3K 3K ee 2 2 he he 3K 2 he SK 2 2 oe ee BytesWritten ComWrt 2 onl 1 r 6 CheckGPIBError Bytes Written ComWrt 2
14. t step in the development of this application is to establish known modem connections The user should set up a local modem connected to the computer with the application program and a remote modem connected to the GPIB 232CT A Although the remote modem must be an external model with auto answering capability the local modem can be either an external or an internal modem The next step is to establish communication between the two modems possibly using a second computer temporarily with the remote modem If both computers are running Windows 3 1 a convenient method to communicate between the two computers would be to use Terminal in the Accessories window Terminal can write to a computer s serial port and will prove helpful in configuring the remote and local modems However any application software that has the ability to write to a computer s serial port can also be used Product and company names are trademarks or trade names of their respective companies 340893A 01 Copyright 1995 National Instruments Corporation All rights reserved February 1995 Remote Modem Setup The remote modem needs to be set up to auto answer after a specified number of rings To determine how to do this consult the technical reference manual for your modem This application note was developed using the Hayes 2400 modem therefore the following settings can be used to configure this type of modem For the Hayes 2400 modem the S register SO must be set to
15. tus has been set Once SRQI has been detected the serial poll byte is read back and available measurement data is retrieved from the instrument See Appendix A for a listing of the ReadAllStatus function BytesWritten ComWrt 2 wait 4096 r 10 Wait for SRQ while InQLen lt 4 All Status returned when SRQ occurs InQLen GetInQLen 2 Check COM2 Input Queue for status ReadAllStatus Read all status information Scan Status s gt d amp hexStat Convert ASCII Status to Hex if hexStat amp 0x1000 Check for SRQ Delay 2 FlushInQ 2 Intialize variables FillBytes spoll 0 5 0 hexSpoll 0 BytesWritten ComWrt 2 rsp 8 r 6 Read back Serial Poll Byte Address 8 BytesRead ComRdTerm 2 spoll 5 13 Read Serial Poll from COM2 Buffer Scan spoll s gt d amp hexSpoll if hexSpoll amp 0x40 BytesWritten ComWrt 2 rd 70 8 r n 9 Read data from device BytesRead ComRdTerm 2 DCbuf 70 13 Read data from COM2 Buffer Delay 2 FlushInQ 2 Intialize variables FillBytes spoll 0 5 0 hexSpoll 0 BytesWritten ComWrt 2 rsp 2 r 6 Read back Serial Poll Byte Address 2 BytesRead ComRdTerm 2 spoll 5 13 Read Serial Poll from COM2 Buffer Scan spoll s gt d amp hexSpoll if hexSpoll amp 0x40 BytesWritten ComWrt 2 rd 70 2 r n 9 Read data from device BytesRead ComRdTerm 2 DCbuf 70 13 Re
16. ws Standard Libraries reference manual SetCTSMode With this function the user can enable Hardware Handshaking In general for Hardware Handshaking to work the serial devices with which you are interfacing must follow a compatible handshaking protocol and the serial cables being used must include the lines to support that handshaking protocol We enable the use of the Clear To Send CTS and the Request To Send RTS handshaking lines using SetCTSMode It returns an error code that can be found in the LabWindows Standard Libraries reference manual ComWrt This function places a specified number of bytes contained in a character buffer into the output queue of a specified serial port It returns the actual number of bytes that were placed in the output queue ComRd This function reads a specified number of bytes from the input queue of a specified port and stores the information in a character buffer It returns an integer value indicating the number of bytes that were actually read FlushInQ FlushOutQ Removes all characters from the Input Output Queue of a specified port GetInQLen This function returns the number of characters in the input queue of the specified port CloseCom Closes a specified COM port and frees the allocated memory buffers for the input and output queues Il
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