That's correct. You have to keep in mind that you have this error for every single bit. And for a complete data byte the errors add up. With this error of 8.5%, this means that the 8th data byte stops 9*8.5% (1 start bit + 8 data bits) = 76.5% of a bit time to early. The UART samples at 50% of the bit time. So it has no chance to receive this data. An error of 5% is very critical. It may work, but it relies on the other side having a completely accurate timing or an error in the same direction. Usually an error should not be more than 2% because you always have to keep in mind that the other partner in the communication may have a similar error in its timing. Regards Frank
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