I am stuck on the following problem. Consider this code:

int main(void)
{
            SysTickInit();
            USART_GPIOInits();
            USART_Inits();
            char data[] = "hello\n";
            for(uint8_t i=0; i<10; i  )
            {
            HAL_UART_Transmit(&Usart1, (uint8_t*)data, strlen(data), 1000);
            }
                while(1){}
}

I try to send hello\n to Hercules in 10 times, but Hercules did not receive what i sent this is what Hercules got , it had þ every the first time I reset the MCU. But , when I used Debugger mode, it did not get any error.

below is transmit function

below is Init function

but want to communicate with fingerprint , but because of this wrong i cant communicate

CodePudding user response：

Change the order of initialization.

From

USART_GPIOInits();
USART_Inits();

to

USART_Inits();
USART_GPIOInits();

UART's default line state is logic high, logic low (start bit) launches a new transfer.

When GPIO is inialized first, with the corresponding peripheral module disabled, most likely you'll gen a logic low level on the TX pin, because there is no one to set it to a logic high (since UART is still disabled). When UART is initialized, it sets the TX line to a logic high (stop bit), and the terminal appication receives it as a broken byte.

Check your schematics

During and after reset CPU outputs are tri-stated. Most likely they'll stay at zero level until the configuration code will do it's job, leading to the same issue - receiving a garbage byte after the reset.

To prevent it, voltage levels on the interface pins must be defined during reset phase with an external pull-up resistor, like 10kOm, from TX and RX pins to VCC.