Crazy UART

[davhak]

Posted on November 21, 2015 at 23:23

Dear All,

I use STM32F415VGTx to establish connection with another node using UART4 (PA0 and PA1 pins) (8bit, 1 stop bit, no parity) using baudrate 10400 (also tried 9600). I have configured USARTs of the same MCU with other nodes without problems. The problem with UART4 is that I can receive bytes from other node correctly but when try to send from STM32F415 a certain byte it seems that it is sent correctly or not depending on the value of the byte. Tracking with oscilloscope/logic analyzer shows that for example sending byte 0x0F works (I can see start bit (low level), then high level for 4 0-bits and again low level for 4 1-bits + stop bit). However sending 0xFF shows on the PA0 (UART.TX pin) as if would sent 0x00 (only start bit is seen then a a continuous high level signal). I have tracked the disassembly code till writing the UART->DR register with the intended byte and saw that DR is written the right byte. I tried to change the device with another similar one but the problem remains. Although it seems a crazy question but is that possible that STM32F415 UART4 (PA0/PA1 pins) has some wrong logic implemented? Thanks a lot for any hint.

[Tesla DeLorean]

Posted on November 22, 2015 at 00:22

Data on a USART is sent LSB first

ie 0x0F -> 00001111 on the wire as 11110000 0x01 -> 00000001 -> 1000000 0xFF -> 11111111 -> 11111111 The RS232 drivers will invert the data, but that's another matter...has some wrong logic implemented? No

[davhak]

Posted on November 22, 2015 at 10:15

Thank you so much!

Very good to know that it's crazy me and not UART.