MicroVAX/VAXstation 2000 (was Re: Back from the fleamarket)

From: Pete Turnbull <pete_at_dunnington.u-net.com>
Date: Tue Jul 3 13:14:58 2001

On Jul 3, 19:56, Jay West wrote:

> > Doh! (to quote the new OED) That should read "RS-423" In any case, it
> > isn't incompatible with RS-232.

RS423 (actually, EIA423) was designed as a compatible replacement for
RS232.

> > > So, is there always an RS-323 console on the DB25?
>
> I'm going from foggy memory here - but isn't the only difference between
> RS232 and RS423 the voltage levels? I think RS232 is something like 0-12
> volts and RS423 is 0-5 volts or something like that. As a result, it
becomes
> a question of tolerances in the circuit. If I recall, on the General
> Automation Zebra Pick machines, they had RS423 ports, and we hooked up
RS232
> devices to them all the time. Almost never did we find an RS232 device
that
> wouldn't work on the RS423 ports. Vague memory here.

Almost any RS232 device should interoperate with almost any RS423 device.
 RS423 uses +/3.6V - +/-6V (IIRC) and usually operates at around +/-5V,
instead of RS232's +/-5V to +/-15V, commonly operated at +/-12V. Also
RS423 controls the slew rate in order to get faster signals further. It's
also specified to be capable of driving several receivers (RS422 is a
similar system but with differential drivers/receivers to go even
faster/further). Unlike RS232, it's purely an electrical standard,
intended to be used in conjunction with other standards (to get
bidirectional interfaces, pinout definitions, etc). Oh, and in theory, it
uses balanced receivers, such that the ground reference for the receiver is
the same ground reference used for the driver; in other words the reciever
signal ground pin is grounded at the transmitting end of the cable only.

I've never had a problem mixing RS232 and RS423. The only possible problem
I can think of is that some RS423 receiver chips are only rated for 10V
inputs, but I've never damaged anything.


-- 
Pete						Peter Turnbull
						Network Manager
						University of York
Received on Tue Jul 03 2001 - 13:14:58 BST

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