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Thread: Bit banging Asynchronous Serial Communication
picon face BY : Bob Ammerman email (remove spam text)

I have had excellent results polling the serial line in a timer interrupt
routine at a multiple of the bit rate.

You need to sample at at least 3x the bit rate, and more is better.

3x works very well with a directly connected async, or when talking to
modern smart modems.

Old 303, 202 or 212 modems often do not accurately recover the timing of the
input signal so I'd want more samples per bit time to help me catch the
'middle' of the bits in this case.

This would also apply in any environment where the bits can be delayed,
especially if rise and fall time are not equal (eg: an 'open-collector' bus

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level

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<00ca01c07b5c$c80bd440$5100a8c0@sciencekit.com> 7bit

See also: www.piclist.com/techref/io/serials.htm?key=serial
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Subject (change) Bit banging Asynchronous Serial Communication

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