The receiver's stop-bit setting needs to be greater than or equal
to the stop bit setting of the transmitter. It is OK for the
transmitter to
You meant less than, not greater than, although, as you noted later,
receivers generally don't have a stop bits setting.
Yes.
send two stop bits and for the receiver to be set for one stop bit.
It won't hurt a thing. Most UARTs use the stop bit setting to
affect only the transmitter (RS-232 sending part of the device).
The receiver will
Delete RS232. (In fact, historically, current loop was used for the
physical interface.)
True, once the mechanical teleprinters fell from grace, current loop
fell by the wayside. (Unless you were connecting to DEC hardware. I
have implemented more than one 20mA current loop to RS-232 converter
in my life.)
handle anything that is at least one bit-time long for a stop bit.
Modern UARTs accept stop bits that are just over half a signalling
unit in length (they sample in the nominal middle, but there is a
limited sampling clock resolution. They need to accept ones that
are strictly shorter than the transmitted ones, because, as we are
talking about asynchronous signalling, they need to be able to cope
with recovering from false start bits and cope with clock rate
differences (more common on mechanical devices, but some electronic
devices rely on these to allow working with convenient crystals.
(When sending asynchronous data over 1200 bps synchronous modems,
sometimes no stop bits could be sent over the wire, if the source
clock was fast, as, being synchronous, there was no option to
shorten the stop bit. Stop bits were re-inserted before creating
the baseband output; I believe they ran the output clock fast to
ensure that this worked.)
You are, of course, correct. I should make sure that I am rigidly
correct when I write and I was being sloppy. Having implemented UARTs
in both software and hardware, and then the protocols to run over them
(I am one of the authors of PPP and the architect for MLPPP) I do have
a modicum of understanding.
Longer stop bits just reduce the maximum rate (characters per
second) that you can send data.
And give better recovery from false start bits - not a problem you
should have on a short piece of wire.
Incidentally, 4800 baud is normally sent with one stop bit. As
noted elsewhere, it is only really for mechanical devices that one
needed longer ones, so it tends to be 110 and below (maybe 300) that
uses 2, or for, 5 unit, Baudot, 1.5.
--
David Woolley
"The Elecraft list is a forum for the discussion of topics related
to Elecraft products and more general topics related ham radio"
List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm>
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73 de Brian, WB6RQN
Brian Lloyd - brian HYPHEN wb6rqn AT lloyd DOT com
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