18 Jun
2013
18 Jun
'13
12:04 p.m.
I'm not
sure what's supposed to be unfriendly about RS-232C. The major
unfriendly part there, it seems to me, is the space in the middle, -3V
to +3V IIRC, for which the logical signal state is undefined.
Well, the problem is that to go from mark to space, you need to swing AT
LEAST 6 volts to be defined. Given that most logic is either 3V or 5V,
that's a bit of a problem.
OTOH, USB is differential, not single-ended. Had you specified RS-422
or RS-486 as a comparison, I would admit that both were competitive with
USB.
Alas very few machines had RS422 ports (the Mac serial port wasn't truely
RS422 IIRC). But covnerting between RS232 and RS422 is a pretty simple
job. I've never seen a single-chip converter, was there one? It's the
sort of thing that Maxim might make, but I've not come across it.
Did you mean RS486? RS485 is the multi-drop RS422, I think.
Every citation of the TIA/EIA/RS-232 spec talks about the range of
voltages used for signaling, but I can't find a citation of "voltage
into what LOAD" defined. Is 2 ohms too small; is 2 megohms too big?
How much current at the specified voltage range is to be supplied by the
driver?
I've not looked, but is it in the appropriate CCITT spec (V.24?) ? That
may well be availble on-line.
-tony