[sci.electronics] Converting RS-422 to RS-232

kujanpa@ccu.umanitoba.ca (12/11/90)

Hi everyone.  Here's my problem:
 
Besides our ethernet, we have a packet
switching network (Develnet).  This network
provides 9600 baud ASCII serial ports to the
mainframe for pc users.

The problem comes when we connect a Mac to
one of these ports.  They will occasionally
lockup to a point, where a linecard has to be
pulled and reset.

I think the problem comes from the Mac (RS-422?)
talking to RS-232.  All we use is a modified cable
to emulate RS-232.  Over long distances the voltage
level coming out of the Mac is very small (ie. not
valid data).

The question: 

Can I build a circuit to change from RS-422 to RS-232?
Can this circuit be powered from the Mac SE port?
Using an external power supply is ok, but if the    
circuit could be powered from the line it would be
great.

Any suggestions, ideas, etc. are more than welcome!
Thanks in advance!
Bob Kujanpaa
kujanpa@ccu.UManitoba.CA


Any suggestion

touch@dsl.cis.upenn.edu (Joe Touch) (12/11/90)

In article <1990Dec10.173757.1162@ccu.umanitoba.ca> kujanpa@ccu.umanitoba.ca writes:
>
>I think the problem comes from the Mac (RS-422?)
>talking to RS-232.  All we use is a modified cable
>to emulate RS-232.  Over long distances the voltage
                          ^^^^^^^^^^^^^^
>level coming out of the Mac is very small (ie. not

The first problem isn't the MAC, its the RS232.  RS232 is
designed to go over less than about 30 yards or so.  RS422
is a balanced-pair differential, which IS capable of
going further.

Joe

tom@bumrl1.bu.edu (Tomislav Lozic) (12/11/90)

In article <1990Dec10.173757.1162@ccu.umanitoba.ca>, kujanpa@ccu.umanitoba.ca writes:
|> 
|> Can I build a circuit to change from RS-422 to RS-232?
|> Can this circuit be powered from the Mac SE port?
|> Using an external power supply is ok, but if the    
|> circuit could be powered from the line it would be
|> great.
|> 

You _can_ build such a circuit. However, if you have better
things to do, you can buy RS-232 to RS-422 converter for
about $10-$15 from B&B electronics. 

Their address is:
	B&B electronics
	P.O.Box 1040
	Ottawa, Illinois 61350

The part is:	RS-232 to RS-422 converter (model 422CFC)

It comes together with a required power-supply (12V, 100mA).
[ I don't know of any such circuit that is powered from SI port ]

NOTE:	To have a good long-distance performance connect the converter
	at RS-232 side and use RS-422 cable. (More expensive but
	also more reliable than long RS-232 cable.)

___________________________________
Tomislav Lozic  <tom@bumrl1.bu.edu>