488.2 GPIB versus VISA

[SteveDD]

Hi,

I have an issue regarding GPIB. I want to do the following:

1. Initialising a Tektronix scope TDS7154 using the provided VISA driver VIs.

2. Sending a couple of pulses with a waveform generator using the 488.2 GPIB functions

3. Reading data from the scope with the VISA drivers.

What I see now is that the scope initialization works fine, also the communication with the waveform generator. But the following VISA communication is very slow. Reading data from the scope takes minutes. Has anybody suggestions what's the problem and how it can be solved? This task is a subroutine in a much bigger program using only the 488.2 GPIB functions. So it would be nice if I don't have to change the way of GPIB communication for one of the two devices.

Tanks,

Steve

[smercurio_fc]

How do you know the problem is with VISA? All that you've said is that reading from the scope is slow. Have you tried reading from it using the lower-level GPIB functions? The problem could be the scope or the way the driver is written. Which driver for the scope did you download?

[Dennis_Knutson]

I doubt that there is any issue with VISA. There is very, very, little extra overhead in using VISA functions. Under the hood, the VISA functions call the low level GPIB functions after all.

The time it takes to read the scope will depend on how many points you are requesting, the sample rate, how long it takes for the scope to be triggered. You have not provided this basic sort of information or attached your code.

p.s. It would probably be advantageous to switch to VISA at some point. It helps prevent obsolence in your code. If you ever switch to Ethernet or USB connections, you would not have to do any rewrites at all or just a minor one.

[SteveDD]

Thanks for the reply.

I am using the NI driver for the Tektronix 7000 series. So far I have not tried to change all VI's in the library to low level GPIB. The scope is working fine if GPIB communication is done only via VISA. Once, low level GPIB is used for a communication with an other device, the scope is getting slow.

[smercurio_fc]

That sounds like the GPIB code is changing a bus parameter or something. Do you see anything like that in the code? Can you upload your code?