PRG switch shorts P23 to ground: what if P23 is an output?

Created Wed, 16 Jul 2014 17:22:16 +0000 by w5uxh

w5uxh

Wed, 16 Jul 2014 17:22:16 +0000

When first testing my new Fubarino SD, I happened to use a sketch from my MAX32 that had P23 assigned as an output for a scope test point.

I later noticed that the PRG switch shorts this pin to ground. Is it thought the chip is robust enough to handle shorting an output to ground, or is it suggested that P23 be defined as an input for all Fubarino projects?

(I will change my test point to another pin and not use P23 as an output in any case, but I am curious if it is actually a concern.)

majenko

Wed, 16 Jul 2014 20:32:38 +0000

I think that was probably overlooked at the design stage. I usually implement the PROG button on my devices with full hardware debouncing, which includes a small resistor (I use 100Ω) on the IO pin, which has the effect of protecting it.

EmbeddedMan

Wed, 16 Jul 2014 20:36:22 +0000

Yup. It would have made more sense to have a series resistor in there. I'll add it to the next rev. My mistake-

However, I've done that by accident too, and never harmed a PIC32 that way.

*Brian

w5uxh

Fri, 18 Jul 2014 16:50:15 +0000

Thanks for the comments. I wired an external PRG switch and did not think to put a resistor even after noticing this! I'll go stick one in now.