But is there
any point to that in modern gear? In fact, why not a PLL to s$
That's great
(and frequently done) if there are enough transitions
[...], but that is typically not the case with asynchronous comms...
you get the start bit, and then you have data (which could be all
zeros).
Indeed. Consider a wire which is in the marking state, then goes to
the spacing state for 312.5 microseconds, returning to mark and staying
there for, say, several milliseconds. (I _think_ I'm using `mark' and
`space' correctly here; they might need switching. By `mark' I mean
the idle state and `space' the other state.) Is that a start bit and
two spacing data bits at 9600 baud (with the rest of the character
being mark bits) or is it a start bit and five spacing data bits (plus
ditto) at 19200 baud? Or is it a framing error at 38400 baud? Or
perhaps just a start bit, with all the data being mark bits, at 3200
baud? Or an entire (8-bit) character of spacing bits at 28800 baud?
Answer: without more information than just the signal on the wire,
there is absolutely no way to tell.
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