Hardware: PXI chasis with 8175 controller and 2 6713s. I send waveform outputs to each 6713 via AO write. Each AO write is in a seperate Case structure. The whole thing is in a while which basically checks for changes to controls. The changes to the waveforms are done inside the Cases with the AO writes.
How can I make the updates to the 6713s happen at the same instant (within 1 milisecond)? Also, do you have an idea how to start a timer at that same instant? (I want to stop the timer with an external change of state.)
For future reference, this type of question actually belongs in the Measurement Devices category, since it deals with the way the 6713 data acquisition board operates. In that category, you will be exposed to similar questions and other users familiar with the board.
Note that the way you can make sure that the boards start at the same time is either by using a start trigger or by synchronizing the update clocks of the two boards.
I am assuming you are using the Intermediate level of AO VIs. With the Easy level (where you just have one VI to output a voltage on the channel), you will be limited to software timing, which will not always be within 1 millisecond. The two ideas above are using hardware timing features of the board.
The start trigger, such as a digital pulse, can be applied to each board, such that each update clock begins at the same time. If the chosen frequency to update are the same, the boards should update at the same time. Alternatively, each board has an internal update clock upon which the channel outputs will be updated. If they have the same clock they will be updated at the same time.
For the timer, if you are talking about starting one of the counters on the 6713, depending on your operation, you can create an appropriate gate signal such that the operation will start and end as you want it. Use the timing diagrams in the LabVIEW Help file for Counter Group Config to see what you want to do. For instance, there is gated event counting, where the counter counts and pauses depending on whether the gate is high or low.
The 6713 boards have counters with the DAQ-STC chip, but there is another chip called the NI-TIO, which is used on the 6601/6602 counter boards. These have a start trigger feature, so you could use the same start trigger for the AO channels as for the counter.
There are several examples that you can look at for these ideas in the LabVIEW >> Examples >> Daq directory. The anlogout directory will have examples for start triggers. To see how to share two clocks between boards, look at the ...\multidev\rtsi_ai.llb\Two E-Series Shared ScanClk.vi example. It's for AI, but you can change it to be AO and route the AO Update signal instead of the AI Scanstart as in the example. To see the counter operations discussed in the LabVIEW Help file discussed above, look in the Counter directory.
I hope this helps! Regards, Geneva L. Applications Engineer National Instruments http://www.ni.com/support