epage
commented
7 years ago Have you tried explicitly starting/stopping the task?
It doesn't look like the example does that but instead shows the different styles of reading. The example probably needs some work to make it more focused on how someone would want to count edges rather than being an API showcase.
Why is this needed? To allow people to optimize their applications, DAQmx implements a state machine but it allows implicit state transitions for ease of use. Most of the time, when an implicit transition happens, the task automatically rolls back after the call. In this case I wonder if the task is automatically stopping after the read call because it automatically started.
I am using a USB-6009 multifunction DAQ with Windows 10 and Python 3.6 as a digital counter on the PFI0 port. The counter tests good in NI MAX. Also, if I read multiple samples, the counter does increment as expected when presented with a 1 kHz square wave.
However, I find that the counter state is reset before every read operation. In other words, if I read 1 sample at a time, I will get the value "0" or "1" as an output. If I read, for example, 1000 samples at once, each sample (more or less, depending on sampling rate) is incrementing as expected.
I am using the example code in ci_count_edges.py, which uses i_channels.add_ci_count_edges_chan().
The underlying NI DAQ MX function is DAQmxReadCounterU32Ex(), which isn't supposed to do this. Therefore, the cause is a bit of a mystery to me.