Hardware Trigger on PXI5154

[Paul Ing]

Hi,

Forgive me if this is quite a stupid question but is it possible to trigger an analog acquisition on one channel of a high speed digitizer (eg: PXI-5154) so that it acquires data while a different channel is high and stops when it goes low (is this a window trigger)?

I will be generating a trigger signal from an FPGA card, but the time at which I need the acquistion to start and how long I need it to last will not be fixed (they will depend on other system variables).  As far as I can see - the best way to achieve this would be to use a digital line out of the FPGA that stays high while I want to acquire data.

It is quite easy for me to create this type of trigger signal from the FPGA - but does the digitizer have a trigger mode that acquires data like this?

Thanks

Paul

[Jennifer O]

Hi Paul,

The NI 5154 does not inherently have the ability to sample variable length records to achieve the window trigger function you are talking about. However, if you are able to create two separate digital signals indicating the start and end of the window,  then you can program the behavior that you are needing.

To achieve this you will need to configure a start and stop (reference) trigger.  You will also need to configure the fetch to read relative to your read pointer.  There are two example programs which will demonstrate these programming steps.

1)niScope EX Fetch Forever (installs with NI-SCOPE).  Read pointer setting is circled.

2)Start and Reference Trigger (link to online example code) 

 

If you wish to acquire multiple records in a row fairly quickly, you can set the number of records to acquire > 1 and configure an Advance Trigger instead of a start trigger.

Hope this helps,

Jennifer O.

Message Edited by Jennifer O on 03-10-2009 09:20 AM

Message Edited by Jennifer O on 03-10-2009 09:21 AM

[Paul Ing]

Jennifer,

It will be easy enough to generate 2 pulses (start and stop) from the FPGA instead of 1 long one - so this should work.

Great.

Thanks

Paul