How do I implement a stop trigger for my 6602 counters?

Question

I currently have the start of data acquistion for two channels syncrhonized with a start trigger. I am doing simple event counting using two seperate counters.
For my start trigger, I use a third counter to generate a single pulse and put the output on the trigger line that the two counters are watching.
Works great! But, I also want to synchronize the stopping of data acquisition for the two channels. I thought this would be simple as configuring a ND_STOP_TRIGGER like I did a ND_START_TRIGGER. But, this is giving me errors.
Does the 6602 not support stop triggering? Am I just out of luck?

Answer 1

Hi there,
this thread is quite old but I'm facing the same problems.
I'm using a PXI-6602 and a PXI-6521 in a PXI-1033 chassis. On the 6521 I create a continuous sample pulse as a counter output. This I route to the PXI_Trig0.
On the 6602 I have two counters set up to continuous edge counting with the external clock configured to PXI_Trig0.
I start counting by setting a internal trigger channel to high which is routed to PXI_Trig1, and this is configured as the start trigger signal for both counters on the 6602 so that they count simultaneously based on their common sample clock.
This works quite good...but I have some problems to stop the counting.
I have to stop counting as soon as I have reached 1024 increments (one revolution of a wheel, signal duty cycle 50 %) on one counter and then I have to check if the other counter have reached at least 48 (duty cycle 50%) or 96 pulses (duty cycle 20% or 80%, depending on the revolution direction).
So far I read the counter value of ctr1 in a loop and if the value is equal to or greater 1024 I stop. Sometimes I miss the value 1024 (how can this happen as I count buffered + continuously?) I make a retry. But I get the impression that even I configured both counters with the same start trigger and sample clock, the counting isn't synchronous. When I try it with two function generators, I works quite good but not perfect. If I connect real life signals, in the lower frequency range (up to 500 1/min of the wheel), I almost always have fewer pulses then necessary, e.g. 88-94 pulses instead of 96. In the upper frequency range (up to 3000 1/min of the wheel), I have way too much pulses, e.g. 122-125 pulses instead of 96.
I use the digital filters of the counter board for both TTL signals.
Does anybody have an idea what I can do on this subject?
Thanks in advance for any help
Regards
Achim