I'm using a USB-6221. I want to count TTL pulses coming from an external device. I want to start/stop counting using an external signal (trigger?).
The following function statements seem logical to me, but they don't work. Can you help?
DAQmxCreateTask ("pulseCnt", &cntTask);
DAQmxCreateCICountEdgesChan (cntTask, "Dev1/ctr0", "", DAQmx_Val_Rising, 0, DAQmx_Val_CountUp);
// The following statement gives this error, "Specified property is not supported by the device or is not applicable to the task".
// Property: "DAQmx_StartTrig_type"
DAQmxCfgDigEdgeStartTrig (cntTask, "/Dev1/PFI10", DAQmx_Val_Rising); // start counting when the TTL count start/stop signal is high
DAQmxCfgDigEdgeRefTrig (cntTask, "/Dev1/PFI0", DAQmx_Val_Falling, 0); // stop counting when TTL count start/stop signal is low.
DAQmxStartTask (cntTask);
How would I know if my device is capable of doing what I described above? What function calls should I use?
Do I need a statement to connect an internal clock to the counter? What statement specifies that?
How do find out where to physically connect the input signal to the USB-6221?
Sorry to ask these seemingly elementary questions but I don't understand in detail how counters work and I can't seem to find a good explaination. Documentation is either too simple or too complicated.
thanks!