27 Jun
2006
27 Jun
'06
7:10 a.m.
It was written....
I've got some equipment here that has RS422 serial
on it - i.e. it uses
differential signal pairs rather than RS232's reference against ground.
I
haven't seen RS422 in a good while. My first exposure to it was an IBM
Series/1 running Pick. The serial connections were all RS422. I scratched my
head when I opened a cable hood for the first time ;)
Question is, can I wire up a cable so that I can use
an RS232 terminal
with this RS422 equipment? (running over a short distance)
No. I believe RS422 has
most of the signals split as pairs, where the logic
true vs. false is the differential between the two pins rather than a set
level. RS232 will not work with this. It'd be like trying to hook up a
differential scsi device to a non-differential scsi device. A cable mod
isn't going to get you there.
We also commonly saw systems (GA Zebra for one) that used RS423, which was
the same as RS232 except the voltage levels which indicated the logic
levels. I *think* that on RS232 the swing was around 12v, and on RS423 it
was around 4v... something along those lines. It was usually possible to
plug an RS232 terminal into an RS423 port depending on the tolerances in
it's design.
Jay West