Subject: RS232 <=> RS422

Jules Richardson julesrichardsonuk at
Tue Jun 27 09:36:49 CDT 2006

Joachim Thiemann wrote:
>> From: Jules Richardson <julesrichardsonuk at>
>> 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.
>> 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)
> A lot of RS422 equipment uses TTL level to create the +/- signal lines
> - hooking it directly to RS232 may blow up your tranceivers, not work,
> or both.  Or, it may work - I think old Macs were tolerant enough to
> do that.

That's interesting - it does look like it's possible to bias & jumper the 
inputs (RXD & CTS) on this equipment so that it protects the receivers. 
Unfortunately the documentation I've got for this particular board isn't high 
on detail; I've got some docs on later revisions though so will check those. 
 From what I gather, it should be jumper-selectable to talk to RS232C, RS422, 
or RS423.



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