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>
> And that start bit depends upon the the stop bit of the previous
> byte. The longer the string transmitted, the more time drift has to
> have an effect.
This is not correct. The stop bit is there to ensure that there is a
level transition between the last data bit and the start bit of the
next byte. Some USARTs will flag an error if the stop bit is not seen
(called a framing error). What happens next depends on the particular
USART.
When the protocol does not include a stop bit, the start bit is
useless and sync bytes need to be injected into the data stream to
allow synchronization. This is the synchronous mode of the uSart as
opposed to the asynchronous mode of the usArt. In synchronous mode
there are no start or stop bits.
Microchip uses the term 'synchronous mode' to mean a serial port with
an external clock e.g. SPI and I2C
> I admit that my experiences have to do with _reading_
> async serial using the RC oscillator where my bit-banged serial reader
> is likely more affected by drift than a hardware UART reading any
serial
> that I'm transmitting.
Asynchronous bit timing is always synchronized with the leading edge
of a start bit (any and all). I would advise you to consider this in
your next bit-banged serial reader.
Regards
Sergio Masci
http://www.xcprod.
.
Earn your degree in as few as 2 years - Advance your career with an AS, BS, MS degree - College-Finder.net.
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