MODM7AE70 ADC VREF pin

[rdabney]

I am updating a system from a MOD5234 to a MODM7AE70. These boards plug into a motherboard in a larger system, all of the pins are backwards compatible (most are just GPIO) except one. Pin P2:5 is a GPIO on the MOD5234 and used as ADC VREF on the MODM7AE70. In our design this is used for a selector knob: either pulled high (3.3V) or active low (GND).

To avoid having to update the motherboard I would like to simply jump P2:5 to a different unused GPIO pin. This would mean that the ADC VREF is being changed somewhat frequently. My question is would this cause any issues like frying the ADC or is there any sort of internal pull down resistor or is this pin driven internally somehow? We are not using the ADC on this project, so I don't care if the ADC doesn't work, just don't want any damage and want to make sure the signal can pass through untouched via that pin.

As far as I can tell it should work, but I am not confident about whether this pin can be driven or affected by something internal to the MODM7AE70.

Thanks

[pbreed]

Have not tried this.
I don't think your using the A/D so messing up Vref should be fine.
Looking at the data sheet I could find a minimum operational vvalue of 1.7V, but could not find anything on vref in the datasheet maximum table.

I think it should be fine.

[johnvan]

I have a similar question regarding this pin. Apparently at some time I decided it was available to use as a GPIO resource. Am I correct in thinking that this is not actually true and there is no way in software to change the functionality of this pin?

...and here I was just getting used to having such a nice *clean* PCB with no green wires...

Thanks,
John

[rdabney]

It was a GPIO on older models, looking at the chip, it says minimum operational value of 1.7V. So, using it as a GPIO (assumedly with ground being low) might cause damage to the chip. I never tried that.

[TomNB]

A good reference for GPIO is the data sheet GPIO column. Vref is an analog input, so it is not GPIO. I've attached a screen shot of the data sheet.