Pin level detection on floating pin nRF51422

[gbrown1966]

hi,

We have a product in production but the PCB-A had been updated with new functionality.

We want to make sure old f/w is not inadvertently loaded to new h/w.

To do this, new PCB-A has an external P.U. removed and we will detect the two h/w revisions by reading the input voltage.

old h/w = P.U. fitted, expect read = 1

new h/w = no P.U.fitted., expect read = 0

I'm seeing that if I configure the input pin with no P.U. I always read a '1' even though a scope shows it is floating at 0v.

If I configure with a P.D. it correctly reads a 0v.

Is there some weak internal P.U. even when you select noP.U.?

thanks in advance

[run_ar]

If you configure a pin as input, but does not configure pull up/down and do not have external pull. You are basically leaving the pin in floating state so it could be either 0 or 1.

[gbrown1966]

Thank you for the confirmation, that makes sense.