HSDIO (pxie-6555) WFM generation + state of static channels

[stardotc]

System: PXIe-6555 card with LabVIEW 2015 (non rt/fpga)

Setup

- 4 DIO channels set up as DYNAMIC - used for SPI. All communication is done via preloaded waveforms.

- All other channels are set up as STATIC.

Problem:

- right before dynamic waveforms are generated, all STATIC channels that are set to HIGH Z Mode get pulled down (driven low) momentarily

- only channels that are set to HIGH Z are affected. The channels that are driven (high or low) remain in their current states.

Not having much luck finding the cause. I have tried using Initial State and Idle State VIs to specifically have each channel retain its current state but no luck. The preloaded waveforms only have data for the 3 DYNAMIC output channels (the 4th Dynamic channel is read only). I'm wondering if maybe HIGH Z mode does not count as a valid state. If anyone have any suggestions, let me know.

 

Thanks!

[stardotc]

Update:

- NI Support was able to verify that INITIATE.VI drives STATIC channels low when they are set to HIGH Z mode. [Test circuit - 10k pull up to 3.3V rail on a single static channel].

- It also appears that this should not be happening per HSDIO documentation. INITIATE.VI should only be valid for dynamic operations and should not have any effect on static channels.

Takeaway:

- PXIe-6555 does not properly support STATIC and DYNAMIC operations in parallel. This might also be the case for other HSDIO cards. I'll try to run the same test on the 6544 to see if it behaves the same way.

Work around:

- I'll have to convert all STATIC channels to DYNAMIC and control them via waveforms. Most likely the only way to have total control of your signal until NI provides a solution/fix.

 

[stardotc]

Update (better late than never):

- Converting STATIC channels to DYNAMIC didn't help much as the problem was with INITIATE.VI. The attached image is the workaround (provided by NI R&D team) for the PPMU cards. HIGH Z channels no longer get pulled down.