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STM32F103 Standby Mode Resets Processor Immediately

Question asked by bergan.brent.001 on Dec 11, 2014

I'm trying to use the STANDBY low power mode on the STM32F103. I have verified that the User Option Bits are set such that IWDG=1, NoReset_STOP=1, NoReset_STBY=1. Therefore the processor should not reset when entering either STOP mode or STANDBY mode.

The following code seems to reset the processor even though NoReset_STBY=1:

void bl_mode_standby(void)
    PWR->CR |=  PWR_CR_CWUF; // In case the pin was high already
    EXTI->PR = 0x007FFFFF;  // Clear any pending EXTI interrupts
    PWR_WakeUpPinCmd(ENABLE);   /* Enable wake from WKUP pin*/

When I check the reason for the reset RCC->CSR = 0x0c00_0000, meaning that it was a Power On Reset & NRST Pin. One thing to note on this HW design, the NRST is not connected (NC), but should have an internal pull-up. Not sure if this is a hint to my issue or not.

Does anyone have an idea why my STANDBY mode is not working and resetting the processor?