Output Voltage on GPIO pins STM3210E-Eval

Posted on May 17, 2011 at 12:53

This was part of a previous post, but I thought I would make it its own.

So doing the GPIO example, I see 1.9V on the output of the pin I toggle high. I am using output pins PF2-PF8 on CN10 now, with Jlink attached. I also removed R97, which raised the reading from 1.8V to 1.9V on PF7.

Looking at the datasheet, on table 45, VOH is listed as outputting Vdd-0.4, minimally 2.4V.

I cannot seem to figure out why i get a low voltage reading. I also want to make sure that it can output 3.3V as I am fabricating a pcb and want to verify that i do not need an extra circuit to drive this low voltage to the desired level. I would also like to figure this out so i can run my experiment on my two eval boards, thanks again!

Gary

Posted on May 17, 2011 at 12:53

PF0 to PF5 are used as A0 to A5, and should no be used for ''IO Toggling experiments'', as those are straight connected to the Flash and SRAM memory.

PF6 to PF9 are connected to LEDs, wich may alter your reading.

You should probe at the MCU side of R96-R97-R98-R99. Probing the Led side will be inside a divider network.

If unsure, just remove those resistors and only one pad will come high.

Also, the GPIO-toggle example code is flicking the LEDs (PF6-PF9), so reading with a multimeter/voltmeter will average the voltage. Wither use a scope, and you should see clear 3.3V square wave, or use a breakpoint in the main ''while'' loop, so it will stop flickering on and off.

Hope that helps,

-Relaxe

Posted on May 17, 2011 at 12:53

Just a follow up...

I was a little confused when i read that an internal 1.8V regulator is used for digital logic, so thats where this thread stemmed from.

Conclusion...When stepping through the program, i do see a solid 3.3Volt output with the voltmeter. When simply pressing run in the debugger, the IOs get averaged. So IOs are ok, Thank you!