USART Transmit Problem

[dhess]

Posted on November 02, 2015 at 21:11

When using the Cube libraries and a baud rate above 260000 on USART1, the serial port needs to be connected to another device or looped back on itself or the code locks up when trying to transmit.  If I lower the baud rate the port works fine and never locks up whether connected or disconnected.  All flow control is turned off so I cannot figure out what would cause this.  

#uart-usart-baud

[Denis Krasutski]

Posted on November 03, 2015 at 14:35

Hello David,

What board are you use? Evalution KIT or custom board? Check value of capacitors on UART lines. BR, Denis

[Tesla DeLorean]

Posted on November 03, 2015 at 14:41

The STM32F4-DISCO has an issue using PA9.

It always helps to be specific about the board and chip in question. ST has dozens of boards, and hundreds of STM32 variants. Common USART to test with are USART2 PA2/PA3, USART6 PC6/PC7

[shawn2]

Posted on November 03, 2015 at 21:44

In my experience, USART1 is only useful for baudrates below 2400.  I've used it in the past for a half-duplex 1200baud signal.  Will generally not function at higher rates than this.

[Tesla DeLorean]

Posted on November 03, 2015 at 22:00

Yes, because there's a very large capacitor hung on PA9, but USART1 should be viable on PB6/PB7