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Signal rise time and fall time requirement

user4090349
Expert 1041 points

Hello

When using UART to transmit data, I would like to know the requirement for the signal rise and fall time.

Do we need to make it less than 10% of the width?

Thanks!

  • 0
    TI__Genius 15345 points

    Hello,

    Is this in relation to one of our devices?

    In terms of RS-485 the usual requirement for rise and fall time is that your max data rate is:

    RS-485 is used a lot of the time to send UART data so you can use that as a rule of thumb.

    Best,

    Chris

  • 0
    Guru 324430 points

    There is no hard limit. A UART receiver samples the voltage near the middle of a bit, so in theory, you can get away with rather slow edges. But in practice, different propagation delays for rising and falling edges or clock differences between transmitter and receiver can shift that point. So the rise/fall times should be as short as possible to reduce the risk of errors, especially if you do not know the accuracy of the clocks of both devices.