07-29-2021 07:54 PM
Hi all,
I am trying to use the following example to acquire data using a start trigger and reference trigger such that I can save a fixed amount of sample before the reference trigger and the rest of the data (total number of samples-data before pretrigger) after the reference trigger happens. I am using NI-USB 6216. The manual says that "Port 1 and port 2 can be used as static digital I/O lines or PFI lines". I checked in NI device-monitor that the digital I/O lines are working when the trigger signal is sent. However, when I run the code, it does not wait for the start trigger before acquiring the data. Does it mean that NI -USB 6216 can not be used with digital triggering?
Thanks
SB
07-30-2021 07:46 AM
Either use Start Digital Edge OR Reference Digitial Edge but not both, not sure how DAQmx reacts to this.
According to the section External Digital Triggers of the manual USB-6216 can work with both kind of triggers.
Regards, Jens
07-30-2021 08:28 AM
Hi Jens,
Thanks for your reply. I did check separately with Start Digital Edge and Reference Digitial Edge. I found that 6216 does not react to any of the triggers at all. However, the digital channels showed the change in voltages when I checked in NI device monitor (digital channel/port 1/line 0-7). PFI1 stands for line 1 and PFI2 stands for line 2.
Hence my doubt was whether 6216 can work with digital triggers at all.
SBH2018
08-02-2021 10:17 AM
Hi,
I can only tell you that the manual states that PFI 0..15 can be used as triggers Analog input (Start Trigger, Reference Trigger, and others).
Regards, Jens
08-02-2021 10:43 AM - edited 08-02-2021 10:45 AM
Hi,
Thanks for your prompt reply. I am a little confused here. Does that mean that the "start digital edge" trigger function and the "reference digital edge" function need to be replaced by something else? I am sure I am missing something but it would help to know a bit more. Please see attached. Also the manual says the PFI channels functionality includes static digital input. Does it mean it can not detect a changing digital level ( like a pulse signal)?
SB
08-02-2021 12:01 PM
@SBH2018 wrote:
Hi,
Thanks for your prompt reply. I am a little confused here. Does that mean that the "start digital edge" trigger function and the "reference digital edge" function need to be replaced by something else? I am sure I am missing something but it would help to know a bit more. Please see attached.
No, those are the correct functions, but as already stated do NOT use both at the same time. Have a look at the examples from the NI example finder (ie. Voltage - finite input.vi). Also keep in mind, that the DAQmx read will currently time-out after a max of 10 sec.
Also the manual says the PFI channels functionality includes static digital input. Does it mean it can not detect a changing digital level ( like a pulse signal)?
It means, that all DIO of that card can only be written or read with software tact (not with a HW timed clock like the AI).
Regards, Jens
08-04-2021 12:17 AM
I don't think I've ever tried setting up a task for both a start trigger AND a reference trigger. I'm not sure which (if any) devices support both simultaneously.
Your OP posting sounds like you *primarily* need a reference trigger so you can define both a # of pre-trigger samples and a total # samples. Have your tried this out without any attempt to configure a start trigger?
If you need both and your device doesn't support both in the same task, there's a likely workaround using a counter task. You'd set up a counter pulse train task that the AI task uses as its sample clock. The counter task would be configured to react to a start trigger, the AI task would continue to use (only) a reference trigger while also using the counter output as its sample clock.
-Kevin P