28 Jul
2006
28 Jul
'06
8:34 a.m.
One could perhaps make a case for the start bit, as it
signals the
start of a character and so conveys some information. But the stop
bit isn't even a bit; it's an empty, information-less time, doing
nothing but demarcating the beginning of the start bit.
Not quite. The time it takes up is important for allowing small
differences in oscillator frequency between sender and receiver to be
tolerated. And having a spacing time there at all is important to
guarantee at least two edges per character.
As long as the signal returned to a spacing level
sometime, I suspect
the actual content of the "stop bit" time is immaterial.
Perhaps theoretically. In practice, if it's not spacing, you'll get
framing errors.
Although I've not tried it, I suspect that 1/2
stop bits would work
fine with most modern UARTs.
I've not tried it either, but I think most UARTs try to sample in the
middle of a bit, so using half a stop bit would risk framing errors if
the receiver is using a slightly slower clock than the sender - or if
the receiver's sampling of the line state takes a significant fraction
of the bit time (which seems not implausible at higher speeds).
You might be able to get away with 2/3 of a stop bit. I wouldn't want
to try it; it seems an awfully small gain (maybe 3% more speed) for a
good deal of complexity and nonstandardization.
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