Jofre,
Mark's suggestion is definitely a simpler and cleaner solution. I've done a pretty similar thing in the past with a 6602 and traditional NI-DAQ. I'd just add two more thoughts to go with his method:
1. You'll want to configure both the counters to be started by the same digital trigger signal so that their time information is synchronized, i.e., they both have the same "0" time.
2. You may need to watch for counter rollover, which occurs in less than a minute at 80 MHz. Not a real big deal, just a little thing to watch for when processing the data.
It could get a little trickier if your trigger signal is relatively rare (once or twice a minute or less). In such cases, you stand the risk of not knowing whether the counter rolled over between triggers or how many times. To help this problem, you could use a slower timebase (probably the 100 kHz) as a source for timestamping the triggers. There are other possibilties requiring the use of additional counters.
Other comments:
- Heed Mark's tip about group # if using Counter Config under traditional NI-DAQ.
- If you aren't heavily committed to traditional NI-DAQ, I'd suggest doing this with DAQmx. I admit that I struggled a while when making the switch but half of the effort was unlearning old ways. I've been using only DAQmx for all new development and I'd venture that for about 80-90% of the functions and features, I prefer it.
- (for academic interest only). It actually *is* possible to use the Z-index reload feature when configuring a counter for position/encoder measurement with a "two-pulse" encoder. You would simply hardwire one of the two inputs to digital ground, and configure the Z-index reload phase to "A LOW B LOW." There would still be two problems for the app in question here.
1. In encoder mode, the up pulse and down pulse must be signals wired to the counter's default SOURCE and AUX/UPDN pins respectively. You would need to somehow bring the internal 80 MHz timebase clock out to your terminal block pins. (I *think* but am not 100% sure that this can be done, but possibly only with DAQmx). Also, the reset signal must likewise be hardwired to the counter's default GATE pin.
2. The Z-index reload pulse seems to operate in a level-sensitive mode rather than edge-sensitive. As I recall from testing, if the trigger pulse remains in a HIGH state during several encoder pulses, the count keeps resetting after each one. One the other hand if it pulses briefly within the time that the A input is HIGH, no reset will occur. (Many industrial measurement encoders are designed to meet these Z-index requirements right out of the box.)
The more I think about it, the more I
REALLY REALLY think there should be a setting that lets you reset a counter to a specific reload value on an EDGE of a software-defined GATE/TRIGGER signal.
Anyway, good luck with things.
-Kevin P.
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