What could make a specific GPIO (PA12 and PA11) on STM32L073V8T6 work when configured as an Input but not work when configured as output?

[oolor.1]

I have a static LCD, a couple of other GPIOs configured as output and SWD which are all working fine. PA12 does not work when I configure it in output mode and i toggle the pin. I have tried using PA11 also with no success. The .ioc file of my project is attached. Thanks.

[waclawek.jan]

> PA12 does not work when I configure it in output mode and i toggle the pin.

Do you do this in debugger? Read out and post all GPIOA registers.

Do you observe *directly* on the pin, e.g. using oscilloscope probe touching the pin?

What is connected to that pin, physically? Is this some kind of a "known good" board such as Nucleo or Disco (in which case make sure you removed all jumpers and solder bridges associated with this pin), or your board?

JW

[S.Ma]

Use debuggr and stop the code while it is running and look at GPIOA registers values.

Possible causes:

• Open drain (put a SW pull-up too see something?)
• GPIOA register clock not activated (all registers are 0x0000)
• Alternate function enabled (as input)
• Analog input

[oolor.1]

Thanks. I'm trying to develop a product with the chip... so it is on my PCB design. The pin is connected to an NPN transistor meant to control an active buzzer. I have removed this transistor so I can run a direct check on the GPIO.

I observed the pin directly with an oscilloscope.

Theses are the readings on the GPIOA registers:

When low:

MODER: 0xA9EAACAB

OTYPER: 0x0

OSPEEDR:0xC000000

PUPDR: 0x24000000

IDR: 0x6000

ODR: 0x0

BSRR: 0x0

LCKR: 0x0

AFR[0]: 0x11001110

AFR[1]: 0x10000111

BRR: 0x0

When high:

MODER: 0xA9EAACAB

OTYPER: 0x0

OSPEEDR:0xC000000

PUPDR: 0x24000000

IDR: 0x7000

ODR: 0x1000

BSRR: 0x0

LCKR: 0x0

AFR[0]: 0x11001110

AFR[1]: 0x10000111

BRR: 0x0

[oolor.1]

Thanks.

• I have tried using S/W pull-up. No changes.
• The register clock for GPIOA is enabled as well as the clock for the other ports I'm using.
• I'll check up on this... though I'm sure the GPIO is configured as output. I don't know if SWD and LCD being enabled on the other pins of the port is causing a conflict.
• Same as above.

[waclawek.jan · Accepted solution]

[oolor.1]

This was the cause of the problem because on my board VDD_USB was floating because I thought it powered only the USB. :see_no_evil_monkey:

Thanks so much.