AnsweredAssumed Answered

9 bit UART and DMA

Question asked by l m on Sep 18, 2017
Latest reply on Sep 19, 2017 by l m


I'm using the UART in 9 bit mode, with the 9th bit being used as an address indication.

I have a version of this working well with 16 bit DMA transfers. Ideally though I want to use 8 bit DMA (byte wide) as all my data is packed for byte wide transfers, and I don't really care about the 9th bit except as an address indicator.

I managed to get this sort of working with byte wide DMA receiving and populating TDR on the transmitter side manually with:

UARTD6.usart->TDR = (uint16_t)addr;


UARTD6.usart->TDR = (uint8_t)val;

UARTD6.usart->TDR = (uint8_t)val;



This works ok.

I would like to replace the sending of the byte wide values with a DMA transfer, but I can't get DMA to transmit correctly though, in that I see incomplete transfers or garbage on the receiving side.


Is this idea achievable? Or is my thinking flawed in trying to send byte wide DMA to the 9 bit UART?

Thanks very much