Modifying Dynamic Generation and Acquisition-Source Synchronous.vi

[Rando]

hi,

I am currently using the PXI-6551 with LabVIEW for high speed digital IO generation and acquisition. My requirement is to use 2 lines for output( to generate 2 clocks) and reading back on 2 lines( serial data). Problem is both the generation and acquisition has to happen at the same time. The output is actually used to clock a chip and at the same time read the input line. Also, this operation should occur only if a trigger signal is received.
I was looking through the examples in LabVIEW and this example is the closest to what I am looking for i.e Dynamic Generation and Acquisition-Source Synchronous.vi.
However, the generation and acquisition does not trigger based on hardware as it is just software trigger. Is it possible to modify the code to trigger on rising edge? Thanks.

rando

[Allen H]

Hi Rando,

The example in its current form is designed to demonstrate how to eliminate round-trip delay through the cable and your device under test. If the connection instructions are followed, the acquisition on the 6551 will begin only when the first sample has propagated all the way through the setup. If you want the acquisition and generation to begin at exactly the same time, you can set the acquisition start trigger to use the same PFI line as the data valid signal.

It sounds like you want both the acquisition and generation to begin based on an external trigger. Keep in mind the trigger delay for generation sessions. The last specification on page 19 of the January 04 655x specifications document says that the delay from trigger to digital data output is 32 sample clock periods + 160 ns. This delay is for the generation only. An acquisition session will start immediately upon a trigger.

So, if you modify the example to configure the generation session for a start trigger (and change the PFI setting as mentioned above), you will get the following:
-- External start trigger is received
-- Maximum of 160 ns + 32 clock cycle delay
-- Data is output by the generation session Data Active event is output.
-- Acquisition Start Trigger is received from Data Active event.

Your acquisition and generation will be synchronized...there will just be a delay after the trigger.

I hope that helps.
Allen