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Setting up complex RTSI triggers

I'm trying to set up a PXI system that contains 2 x PXI-6259 DAQ modules and a single channel CAN module. The aim is to set up stimuli / take measurements on the DAQs, then encode the settings and measurements onto a series of CAN messages, and transmit these to another PC which will log the data along with other CAN data sent from the DUTs. The timing of these operations are important - this stimulus/measurement/CAN transmission needs to happen at 20mS intervals. I've been experimenting with RTSI and the examples provided by NI, but I can't find a method of getting the CAN module to send multiple frames on receipt of a single RTSI event (i.e. a 50Hz counter routed to one of the RTSI signals). Maybe this isn't possible, so my other idea would be to try to generate a 'complex' RTSI signal from the DAQ card. i.e. a combination of a 50Hz counter to provide the 20mS starting point, then a series of 4 or 5 pulses to trigger the transmissions of the CAN messages. Does anyone know if it's possible to build up combinational RTSI trigger signals?

Many Thanks...
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slaine,

I don't have a full answer, but maybe about half of one. The first point to emphasize is that any hw-timed signal you'd like to share across RTSI needs to be created by the hw resources of your boards (internal clocks, programmable counter/timers).

Between your 2 DAQ cards you have 4 counter/timers that can be used to generate the timing signal pattern you need. If I understand correctly, you should be able to accomplish the clock and pulse pattern with either 2 or 3 counters. These counter outputs can easily be exported to the RTSI bus to be shared. I don't know CAN well enough to comment on syncing the messages with specific RTSI pulses.

Example 1: generate a 250 Hz pulse train with one counter and then create a 50 Hz pulse train on another counter by "dividing down" the 250 Hz clock. This would necessarily space the messages equally in time at 4 msec.

Example 2 (if you need bursts of messages spaced, say, 1 msec apart): create a 50 Hz pulse train and a 1 kHz pulse train that uses the 50 Hz pulse train as a "Pause Trigger." The result of this "Pause Trigger" mode is similar to a logical AND of the two pulse train outputs. By carefully choosing the "high time" of the 50 Hz pulse train, you can choose the # of 1-msec-spaced messages to be sent.


-Kevin P.
CAUTION! New LabVIEW adopters -- it's too late for me, but you *can* save yourself. The new subscription policy for LabVIEW puts NI's hand in your wallet for the rest of your working life. Are you sure you're *that* dedicated to LabVIEW? (Summary of my reasons in this post, part of a voluminous thread of mostly complaints starting here).
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Slaine,

This is possible, all RTSI connections have direct routes for this board to PFI 12 and 13 (CTR 0/1 OUT). Generating a pulse train from a counter is rather straight forward so look into the DAQmx examples in Help->Find Examples for this.

Regarding the CAN issue have a look at this tutorial :

Synchronizing High-Speed CAN Transmissions with Data Acquisition Measurements
http://zone.ni.com/devzone/conceptd.nsf/webmain/c0a12a2efc24181f86256c560071c5a8

This uses traditional DAQ but DAQmx does all the routing for you. See this tutorial :

Timing and Synchronization Features of NI-DAQmx
http://zone.ni.com/devzone/conceptd.nsf/webmain/2638A8DA4E4CFD1F86256D250070C093

As you are using PXI ensure you have identified the chassis, this will create the RTSI cable for you or tell the driver to use the PXI backplain for routing the signals.

Hope this helps, Kind Regards


Steven Bird
Applications Engineer
National Instruments
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You may find this utility helpful in setting up your timing and triggering application:
http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=F4023DE6E9FD4F39E0340003BA7CCD71
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