I am using the STMG0B1RET on a custom, battery-powered board. During normal operation pin PC4 is used as UART1 (with an external pull-up resistor). In Standby Mode pin PC4 must be LOW in order to shut down the external device. For this I convert PC4 to GPIO and configure it for pull-down in Standby Mode to achieve the 0V at the output.
It is not working. When the HAL function HAL_PWR_EnterSTANDBYMode() is called the output goes HI.
I studied several posts and discussions about this issue, but no success yet.
The below is the latest code snipped. Wakeup pin 6 is used to exit Standby Mode (that works).
This line seems to pull the output to HI. Why?
SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk;
What else can we try? Thank you!!
/* Convert UART1 IO to a GPIO */
GPIO_InitTypeDef GPIO_InitStruct = {0};
HAL_GPIO_WritePin(UART1_GPIO_Port, UART1_Pin, GPIO_PIN_RESET);
/*Configure GPIO pin : UART1_Pin */
GPIO_InitStruct.Pin = UART1_Pin;
GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
GPIO_InitStruct.Pull = GPIO_NOPULL;
GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
HAL_GPIO_Init(UART1_GPIO_Port, &GPIO_InitStruct);
PWR->PDCRC = PWR_PDCRC_PD4; // Set pull-ups for standby modes
PWR->CR4 = PWR_CR4_WP6; // Set wakeup pin 6 to low level
PWR->CR3 = PWR_CR3_APC | PWR_CR3_EWUP6; // Enable pin pull configurations and wakeup pins
PWR->SCR = PWR_SCR_CWUF; // Clear wakeup flags
// Configure MCU low-power mode for CPU deep sleep mode
PWR->CR1 |= PWR_LOWPOWERMODE_STANDBY;
(void)PWR->CR1; // Ensure that the previous PWR register operations have been completed
// Configure CPU core
SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk; // Enable CPU deep sleep mode
// Enter low-power mode
for (;;) {
__DSB();
__WFI();
}
