"David Harper" wrote in message
m...
Ok, I have one more additional question. :-)

Sorry, I skipped something on the previous response.

I answered for ASYNCHRONOUS serial such as RTTY or async ASCII.

Some protocols, such as packet, use SYNCHRONOUS serial. Synchronous serial
is a lot harder to receive. There are no start and stop bits, so the
protocol doesn't involve that part of the overhead that async uses.

There are several synchronous protocols, but they mostly involve two
characteristics.... first, there is some mechanism for the receiver to
recover the clock. Frequently, the clock is embedded in the data, although
is could be sent over another channel. This allows the receiver to know the
bit boundaries. Every so often (typically every data packet) a special
pattern is sent that allows the receiver to identify the character
boundaries. In the common protocols, such as X.25 (or AX.25), there is also
a prohibition against sending too many of the same bit in a row. Special
procedures are invoked if this happens in the data.

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