RS-232 Tx / Rx monitoring LEDs?

Mouse mouse at Rodents-Montreal.ORG
Thu Aug 20 12:23:21 CDT 2015

> A consideration with RS232 is that the signals swing to either side of 0, so$

It's been a while since I read the spec, but I think it's -3 to -20
volts one way and +3 to +20 the other, with the -3 to +3 range
deliberately left ambiguous.  I think there are slew rate limits, too,
but I don't recall what they are even approximately.

Of course, serial lines are normally run over unshielded wires with a
single shared signal ground, so, for noise tolerance, transmitters
usually drive the outputs substantially beyond 3V either side of
ground.  (There are also short-circuit tolerance specs which mean you
don't want your output impedance to be too low, either.  I think it's
something like, any pins or ccombinations of pins may be shorted to one
another and/or any voltage or voltages from -20 to +20 indefinitely
without damage.)

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