Inverted DAC output

[bridges]

Posted on May 30, 2014 at 17:16

Any ideas what would cause a STM32F4 Discovery board to suddenly invert the DAC output, such that 0 gives 3V and 4095 gives 0V? This does not seem to be a programming issue as the identical program worked fine prior (and on other boards). It also does not appear to be a single bad board, it has happened to me on two boards. The issue seems to unrecoverable, reloading a program, cycling power, etc do not fix it.

I had been hooking and unhooking leads, so it is possible a stray voltage went somewhere bad, but I would still like to understand the mechanism. The boards work fine otherwise (including the ADCs).Thanks.

[frankmeyer9]

Posted on June 02, 2014 at 13:12

The DAC output would appear inverted if you reference (measure) it in regard to VDDA, and not to GND. So it might be a wiring issue.

[etheory]

Are you using the buffered (non-inverting) or the unbuffered output driving a virtual earth inverting opamp (inverting) output? Because depending on your choice, obviously one will invert compared to the other, which is the most likely explanation.