Posted on June 15, 2017 at 12:14
#stm32f103cb #gpio #input
Hi,
I encountered a problem with STM32F103CB when setting PB8 as pull-up input.
In hardware, PB8 is externally pulled up to 3.3V. And it is set as pull-up input. However, after MCU start, it is being detected as low continuously (By reading GPIOB->IDR). At this point, whenever this pin is grounded externally, this unable-to-detect-level-high issue will disappear.
I have also test PB5 to PB9, same setting but only PB8 experiences this problem.
One other weird thing is that if I set PB8 as open-drain output low before setting it as pull-up input. The issue will disappear.
This issue does not appear in every chip. Actually it appear in a low quantity of chips. But the error on PB8 is consistent among the failing chips. Any idea on what could go wrong?
Thanks!
--------------------Update-----------------------------
Here is the test code:
int i;
GPIO_TypeDef a; RCC->APB2ENR |= RCC_APB2ENR_IOPBEN; GPIOB->BSRR = (0x1 << 8); GPIOB->CRH &= ~(0xF << 0); GPIOB->CRH |= (0x8 << 0); while (1) { a = *GPIOB; i = GPIOB->IDR; }That's every thing in the main function. In debug mode, when I stop at ''a = *GPIOB'', below is the variable watch in Keil.
#stm32f103cb #gpio #input
