Use external pulse in PFI as clock for sampling

[PBal]

I have an analog signal connected to the 6356 card via SCB68 on PXIe chassis, using Labview 2017.

I am able to acquire data from it using the internal clock for the sample clock.

I have a TI microcontroller GPIO output that pulses periodically at half a millisecond time period (500uS)

I need to sample the earlier analog signal at the rising edge of the pulse from the TI Microcontroller.

I read online that I can connect the GPIO output to PFI line and use it as an external clock source so that data can be acquired from analog pin at the rising edge of the GPIO pulse.

I read in the 6356 documentation that the PFI pins are by default high impedence input so it should not draw current from the MCU GPIO pin.

There is a caution on not to connect the PFI pins to voltage source when PFI pins are in output mode.

I have an oscilloscope parallely connected to the GPIO pin to monitor its state.

The pulse from the GPIO pin is correct at 500uS period, as I can see from the oscilloscope.

However when I connect the GPIO pin to PFI0, the pulse disappears on the scope and comes to ground.

What am I doing wrong? Is there anyway to ensure that the PFI0 pin is in high impedence input mode?

[santo_13]

If you configure PFI0 as the Sample Clock source, it should automatically put the PFI into input mode (high-impedance). At idle state, it will return back to default which may be the output mode and digital Low.

[PBal]

Santosh, Thank you for your reply.

Can you please tell how to configure PFI0 as sample clock source.

Right now I am selecting PFI0 as the clock source in the sampling clock block in the VI.

Any additional step needs to be done to configure PFI0 as high impedence input?

[santo_13]

Yeah, configuring the Configure Timing API with PFI0 as a clock source should do the trick. Just making sure, did you connect the grounds together?

[PBal]

Many thanks for your reply.

Yes , I connected the ground from the micro controller to the D_GRND terminal closest to the PFI0 terminal in SCB68.

Still, the signal on the GPIO output from the MCU flat lines once I connect it to the PFI pin.

Am I not supposed to connect the ground?

[PBal · Accepted solution]

Original question poser here.

When I changed the SCB 68 terminal, the existing set up worked without modification.

I guess the SCB 68 I used was faulty.

Thank you for your time in answering the query.

PBal.