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Original question:

TMS320F28069M: SCI UART baud rate tolerance

TMS320F28069M: SCI start bit and stop bit length

Julia Li
Expert 4755 points

Part Number: TMS320F28069M

Dear champs,

I checked some E2E threads and I know that we do not have an exact number about SCI baud rate error, we encourage a tolerance of less than 3% error. Customer's SCI data bits can achieve less than 3% error. But the lengths of start bit and stop bit are not stable. For example, when the baud rate is 9600, the stop bit length is 160us and the start bit length is 140us. How does C2000 ensure that the stop bit and start bit are correctly identified? Thanks!

Best Regards,

Julia

  • +1
    TI__Mastermind 25210 points

    Hi Julia, 

    The bits in SCI are sampled by majority voting as described in the TRM section 13.10 SCI Communication Format:

    This majority voting is how there is some error tolerance with SCI (as in, there is a cushion of SCICLK pulses around the majority voting). The only concern is if the start bit is long enough where it corrupts the majority voting of that first data bit (and the rest of the bits), which you can think of as a shift in reading frame. But as long as the start bit meets the 4 consecutive 0 SCICLK pulses (and is not so long that it affects the data) and the stop bit meets the majority voting, they will be identified correctly. The stop bit can be longer since it only depends on the 4, 5, 6 SCICLK pulses. 

    Best Regards,

    Allison