Xref: utzoo sci.electronics:8521 comp.lsi:862
Newsgroups: sci.electronics,comp.lsi
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: RS-232 5V (???), reference needed
Message-ID: <1989Nov9.204337.9914@utzoo.uucp>
Organization: U of Toronto Zoology
References: <9820@etana.tut.fi>
Date: Thu, 9 Nov 89 20:43:37 GMT

In article <9820@etana.tut.fi> nurmi@tut.fi (Nurmi Jari) writes:
>I am looking for a standard serial interface which could be implemented
>using 0-5V CMOS devices...

Well, the Maxim MAX232 family implements real RS232C using a +5 supply,
and as I recall it's a CMOS device...  It has its own voltage multiplier
and inverter to turn +5 into +-9.  This is by far the simplest and least
painful solution unless you have special constraints.  If "using 0-5V
CMOS devices" means "on my own CMOS chip" or "with 4000-series chips only"
or "with very low power consumption", then you do.  Consider RS422, which
is differential (2 wires per signal) but can be done with +5 only if my
memory is correct.  RS423 is sort of a modern RS232 using +-5.  I can't
think of any non-differential +5-only form offhand.

Although the RS232 standard says (-3)-(+3) is the minimum swing, many
RS232 receivers will react acceptably to a 0-3V swing.  That's definitely
non-standard, though.
-- 
A bit of tolerance is worth a  |     Henry Spencer at U of Toronto Zoology
megabyte of flaming.           | uunet!attcan!utzoo!henry henry@zoo.toronto.edu