UART Framing Error on STM32F1

[tonyblake9]

Posted on May 19, 2017 at 14:32

Hi,

I have an STM32F1 and am running the UART printf example from the standard peripheral library. I've modified the code to allow me to use USART3 (I'm using a custom pcba and only USART3 is wired to a connector mounted on the board). I've connected USART3 to a serial terminal on my computer (RealTerm) using an FTDI USB-UART converter. I am successfully receiving data from the UART but the data is incorrect and the terminal complains of a framing error. I am transmitting a single character 'T' but am receiving unknown data:

I am convinced that there is a problem in my code, most likely in how I have configured USART3, but am not sure where. I have checked that my baud rate etc is good in both the code, cable and terminal.

Can anyone help me with this? What is the most likely reason I am not receiving the correct data?

Cheers,

Tony

#stm32-f1 #framing-error #usart

[Tesla DeLorean]

Posted on May 19, 2017 at 20:13

Baud rate wrong (bad assumption about clock sources and speeds)

Wrong levels. Device outputs CMOS level, not RS232 level, which are higher and inverted.

Use 2-stop bits, creates a larger inter-symbol gap, if synchronization is an issue.

Try outputting a stream of 'U' characters and measuring bit timing on a scope.

Make sure to test for TXE before outputting to data register.

[tonyblake9]

Posted on May 22, 2017 at 14:12

Hi Clive,

As I said, I'm convinced that the problem in my code. Can you see anything wrong here:

void USART3_Config(void)

{ GPIO_InitTypeDef GPIO_InitStruct; NVIC_InitTypeDef NVIC_InitStructure; USART_InitTypeDef USART_InitStruct; // 1) Clock Config RCC_APB2PeriphClockCmd(RCC_APB1Periph_USART3,ENABLE); RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB,ENABLE); RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO, ENABLE);

// 2) GPIO Config

GPIO_InitStruct.GPIO_Pin = GPIO_Pin_10; // USART3 TX GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF_PP; GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz; GPIO_Init(GPIOB, &GPIO_InitStruct); GPIO_InitStruct.GPIO_Pin = GPIO_Pin_11; // USART3 RX GPIO_InitStruct.GPIO_Mode = GPIO_Mode_IN_FLOATING; GPIO_Init(GPIOB, &GPIO_InitStruct);

// 3) NVIC Config

NVIC_InitStructure.NVIC_IRQChannel = USART3_IRQChannel; NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority=0; NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0; NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE; NVIC_Init(&NVIC_InitStructure); // 4) USART Struct Config USART_InitStruct.USART_BaudRate = 115200; USART_InitStruct.USART_StopBits = USART_StopBits_1; USART_InitStruct.USART_WordLength = USART_WordLength_8b; USART_InitStruct.USART_Parity = USART_Parity_No; USART_InitStruct.USART_HardwareFlowControl = USART_HardwareFlowControl_None; USART_InitStruct.USART_Mode = USART_Mode_Rx | USART_Mode_Tx; USART_Init(USART3, &USART_InitStruct); USART_Cmd(USART3, ENABLE); }

[Tesla DeLorean · Accepted solution]

Posted on May 22, 2017 at 14:18

USART3 is not on APB2

[tonyblake9]

Posted on May 22, 2017 at 15:29

Yep that was the problem, should have been on APB1.

Thank you!