Hello,
We have run into a weird behaviour with the STM32G070KB. With PA8 defined as an input with internal pullup and PA9 as output push-pull.
When PA9 is at low level and PA8 unconnected, PA8 is at VCC (3.3V) as expected.
When PA9 is at high level, PA8 drops to 0.29V. Adding an external 10k pull up raises PA8 to around 1V.
Actually after more tests, leaving PA9 as an input and driving it externally to VCC also makes PA8 to drop.
We are using a custom board, but at this point after unsoldering components and cutting traces, both PA8 and PA9 are not connected to anything so this is not due to external components.
This code sample reproduces the behaviour :
int main(void)
{
SET_BIT(RCC->IOPENR, RCC_IOPENR_GPIOAEN);
//Set PA8 as input pull up
GPIOA->MODER &= ~GPIO_MODER_MODE8;
GPIOA->PUPDR |= GPIO_PUPDR_PUPD8_0;
//PA8 reads 3.3V as it should
//Set PA9 as output push-pull low
GPIOA->MODER &= ~GPIO_MODER_MODE9_1;
GPIOA->OTYPER &= ~GPIO_OTYPER_OT9;
GPIOA->BSRR = GPIO_BSRR_BS9;
//PA8 reads 0.29V at this point
while (1)
{
}
return 0;
}
Why is this happening ? How can we avoid it ?
Best regards,
Geofrey MARCEL
