PCMCIA-GPIB

[Delgados]

I´m using a PCMCIA-GPIB data adquisition card. I get a correct comunication with my instrument, being able to control it. but I have some problems on the adquisition:

Sometimes the adquired data is not completed or even I didn´t get anything. This happens also with reallly short commands. The timeout parameter is on 300 secs. It should be big enough for the amount of data.

When I send the next command, the data from the previous one appears on the output file.

Any help will be really appreciated.

Juan

[Dennis_Knutson]

If you are getting results from a previous query, then it sounds like you are not specifying a high enough byte count for your VISA Read. How did you determine the byte count for each command? You can safely specify some large number because the VISa Read will terminate automaticaly when EOI is detected.

[Delgados]

Thanks Dennis,

How can I specify a larger number for the byte count?

[Dennis_Knutson]

Just put a bigger number there. How are you specifying the count now? I hope you're not wiring the return count from VISA Write to the Byte Count of VISA Read.

Message Edited by Dennis Knutson on 06-21-2006 10:38 AM

[Delgados]

In the controls of my GPIB-PCMCIA card I couldn´t find how to modify the byte count. Is the control of the byte count a part of the data adquisition software? The program I use to control the instrument was made by the instrument manufacter, so I can not really play with it.

Another strange feature of my communication is that when I do a "Scan for instruments" the NI meassurement and control software says:

Primary Address = 5                The device did not respond to a *IDN query

However when I try to control it using that Primary Addres I get no response, but with a PA=0   I can make the communication (with failures).

Thanks again,

Juan

[Dennis_Knutson]

Well, I completely misunderstood the situation. I assumed that you were writing your own program to talk to an instrument and I also assumed you were using LabVIEW. If you are working with a program provided by someone else, then you can't change the byte count in that program.

The message about not responding to the *IDN? query may only mean that the instrument doesn't support that command. Writing commands to PA0 means that you are writing to the GPIB card. If MAX finds an instrument at address 5, you should be able to talk to it assuming that you are sending the correct commands.

It occurs to me though, that since the instrument doesn't respond to the *IDN?, that it might be something very old. Some older instruments weren't real friendly to use. I have seen instruments that require additional characters besides just the standard EOI. Sometimes you also have to append a CR, LF, or both at the end of a command. Do you have the instrument's manual that you can look this up? What is the instrument?

[Delgados]

The instrument is a System 8400, in fact really old:  http://www.pressuresystems.com/8400sp1.html 

the instructions manual says that: "The SP sats the EOI line with the last byte of the response packet (if GPIB host link used)" , and nothing else about CR or LF...