Jinx,

On Sat, 13 Jan 2007 17:50:46 +1300, Jinx wrote:

> > The re-sync happens on the start bit of every byte.
> > 1.7% isn't enough to cause a problem.
> 
> Are there not some protocols/methods that may not explicitly
> re-synch or am I thinking of something else ?

Far be it for me to predict what you are thinking (I don't even know what *I'm* thinking! :-) but I do think you are thinking of something else.  The 
normal serial comms that we're used to is Asynchronous (the "A" in UART and USART) which means that there is no explicit synchronisation between 
transmitter and receiver - there's no "Clock" line.  So the receiver has to detect the bit positions from the data itself, which is what the Start Bit is 
for - knowing the bit length and when the byte starts, the receiver can recover the data, with the Stop Bit acting as a check that it got it right.  It's 
not infallible of course...  But the upshot is that each byte is re-synchronised automatically, so as long as the timing doesn't drift more than half bit in 
a byte (because most UARTs sample the middle of the bit) and there's enough time between bytes that an overrun on one doesn't cause the next 
Start Bit to be missed, it works pretty well.  That last point needs to be emphasised:  if you're not sure of your timing, leaving a bit of a gap (or vice 
versa!) in between the bytes is a Good Thing, even though it slows down the transmission a tad.

Cheers,


Howard Winter
St.Albans, England


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