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From: psfales@cbnewsc.att.com (Peter Fales)
Newsgroups: sci.electronics
Subject: Re: Help Needed: TTL<->RS232 without -12vdc
Keywords: RS232, TTL, level shifting
Message-ID: <1990Aug26.234711.23808@cbnewsc.att.com>
Date: 26 Aug 90 23:47:11 GMT
References: <7574@scolex.sco.COM> <1990Aug25.232127.4269@hayes.fai.alaska.edu>
Organization: AT&T Bell Laboratories
Lines: 25

In article <7574@scolex.sco.COM>, deanr@sco.COM (Dean Reece) writes...
> 
>Hi, I need some help with RS232 drivers/receivers
>I'm building a project that needs a standard RS232 port, but only has
>available supplies of +5, +12, and +24 volts.  I thought that I
>might be able to use the 0(GND), +12, and +24 kinda like the +/- 12v supply
>usually called for.  I couldn't think of any trivial way to do this,

This may or may not be what you are looking for, but if you just want to
talk to a single specific RS-232 device, I have had good luck using a
TTL inverter as an RS-232 driver.

I don't recommend this technnique for a commercial product (or anything
that someone besides yourself might use), but many RS-232 receivers will
accept 5 volts as logic 0 and 0 volts as a logic 1 (despite the fact that
the spec says the that the logic 1 must be more negative than -3 volts).

Again, don't sell it and dont't blame me if it doesn't work, but I have gone 
up to 9600 baud over short distances without problems.

-- 
Peter Fales			AT&T, Room 5B-420
N9IYJ            		2000 N. Naperville Rd.
UUCP:	...att!ihlpb!psfales	Naperville, IL 60566
Domain: psfales@ihlpb.att.com	work:	(708) 979-8031