Is the IRQ pin on the MCC128 necessary for normal operation?

[dzajac]

My setup is using an MCC128 hat for general purpose data acquisition, as well as a separate hat for RS485-based sensors. I ran into an issue where the RS485 hat uses the Raspberry Pi's SPI1 interface, which conflicts with the IRQ pin (GPIO20) used on the MCC128. Is the IRQ pin strictly necessary for normal operation? If it is necessary, would it be possible to change which pin is used?

[Jeffrey]

Per the Developer, the IRQ pins on the 128 and 172 (both share GPIO20) are there in case we want to optimize transfers in the future, but we do not currently use them.  Perhaps you have another signal present on that pin from something else? 

[Dave G]

Is this still the case that the IRQ is not used?  I have the same issue that it will conflict with another hat.

[Fausto]

Hello @Dave G.  

The conflict between the MCC 128 and your other hat is more likely a conflict with sharing the SPI interface. 

https://mccdaq.github.io/daqhats/_static/esmcc128.pdf

 

 

On our end, third-party devices have conflicts when attempting to share the SPI with our MCC DAQ HATs.

Regards,

Fausto

[Dave G]

Thanks, Fausto.  I don't have a conflict yet.  I haven't purchased the hats.  I am trying to do my homework first and not buy stuff that isn't going to work.  The other board in question is an audio hat.  It uses the PCM interface, not the SPI.  However, for whatever reason, you guys chose to use GPIO20 for IRQ, which is dedicated as PCM_DIN.

So, I need to know, is the MCC128 going to interfere with GPIO20 or not?

Thanks,

Dave G.

[Fausto]

Hello @Dave G.

The GPIO20 pin connects to an open-drain output on the MCC 128 MCU but the firmware currently sets that pin to high impedance and does not drive it low.  There should be no conflict with another board using that signal pin. 

Regards,

Fausto

[Dave G]

Thank-you!