STM32G071 PORTD Pullups

KMill · ‎2026-02-24

I'm connecting a 12-Way rotary switch to an STM32G071 as shown:

Board room is extremely limited, so I'm using the MCUs built in Pull Ups.

However when I read the lowest four bits of PORTD->IDR (for switch positions 7,8,9 and 10) it reads 0xA when it should read 0xF (The rotary is at position 1, so PORTD0:3 should all be pulled up).

Cube MX confirms PULL UP is enabled for all switch inputs:

The only other peripherals enabled on the chip are DAC output on PA4 and GPIO Output on PA15

I have carefully examined the board, and there are definitely no shorts to ground, and the switch it operating perfectly.

If I measure the voltage on all the PORTD0:3 pins, all are pulled up to 3.3v except PD0 and PD2, when they should be.

Any suggestions?

Andrew Neil · ‎2026-02-24

PORT D Read errors.

A complex system that works is invariably found to have evolved from a simple system that worked.
A complex system designed from scratch never works and cannot be patched up to make it work.

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Andrew Neil · ‎2026-02-24

PORT D Read errors.

A complex system that works is invariably found to have evolved from a simple system that worked.
A complex system designed from scratch never works and cannot be patched up to make it work.

KMill · ‎2026-02-24

@Andrew Neil you'd think I would have remembered that!

Ozone · ‎2026-02-24

> Cube MX confirms PULL UP is enabled for all switch inputs:

But does the generated code really enable all pull-ups ?

Andrew Neil · ‎2026-02-24

Ha ha! I hadn't noticed that was also you!

A complex system that works is invariably found to have evolved from a simple system that worked.
A complex system designed from scratch never works and cannot be patched up to make it work.

mƎALLEm · ‎2026-02-24

@KMill wrote:

@Andrew Neil you'd think I would have remembered that!

:D

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