At register level, there is an IDR (input data register) and ODR (output data register). They both work independently, i.e. you can read back the IO value with IDR while in output "mode".
This works with HAL as well:
So you might setup a GPIO pin as open-drain output with a pull-up in the chip configuration or code:
/*Configure GPIO pin : PA0 */
GPIO_InitStruct.Pin = GPIO_PIN_0;
GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_OD;
GPIO_InitStruct.Pull = GPIO_PULLUP;
GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
and read back the current pin level using
GPIO_PinState val = HAL_GPIO_ReadPin(GPIOA, GPIO_PIN_0);
and change the output level using
HAL_GPIO_WritePin(GPIOA, GPIO_PIN_0, val );
as you like.
hth
KnarfB
