[comp.lsi] RS-232 5V

nurmi@haapana.tut.fi (Nurmi Jari) (11/09/89)

I am looking for a standard serial interface which could be implemented
using 0-5V CMOS devices. I have heard some second hand information that
there EXISTS some RS-232-xxx standard that might do.

If someone out there knows such standard, please let me know! I would be
pleased to have a) a verification of the existence of the 5V version
b) the identification of the standard (by what name can I find it) and then
c) what is the reference where I can read the specifications of it.

Please save me a lot of work!

Jari Nurmi                        # Tampere University of Technology 
                                  #     /Signal Processing Laboratory
nurmi@tut.fi                      # PO Box 527, SF-33101 Tampere, Finland
(nurmi@tut.UUCP   mcvax!tut!nurmi)# tel: +358 31 162 697  fax: 162 913

henry@utzoo.uucp (Henry Spencer) (11/10/89)

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

phil@ingr.com (Phil Johnson) (11/10/89)

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. I have heard some second hand information that
>there EXISTS some RS-232-xxx standard that might do.
>

     Maxim Integrated Products
     120 San Gabriel Dr.
     Sunnyvale, California 94086
     USA
     (408) 737-7600

  Manufactures a series of RS-232 transceivers that use +5vdc only.  There
  are about 20-30 different chips in the MAX 2xx series, each with a different
  number of drivers, receivers, external caps, and features.  The RS-232
  voltages (+- 10 vdc) are derived from a charge-pump circuit developed by 
  Maxim.

  I have used these chips on several projects and it really saves time and 
  space when you don't have to worry about an extra power supply just for the
  serial interface. 

  (NOPE: I don't work for, receive compensation from, but use Maxim products)
  (If they would like to send me any sample I'll take them.) 8-{)


-- 
Philip E. Johnson                    UUCP:  usenet!ingr!b3!sys_7a!phil
MY words,                           VOICE:  (205) 772-2497
MY opinion!

josef@peun11.uucp (Moellers) (11/14/89)

nurmi@haapana.tut.fi (Nurmi Jari) writes:


>I am looking for a standard serial interface which could be implemented
>using 0-5V CMOS devices. I have heard some second hand information that
>there EXISTS some RS-232-xxx standard that might do.

>If someone out there knows such standard, please let me know! I would be
>pleased to have a) a verification of the existence of the 5V version
>b) the identification of the standard (by what name can I find it) and then
>c) what is the reference where I can read the specifications of it.

There are two ways to get away with 5V only:

1 Stick with the "original" RS232C (a.k.a. V.28) and use chips
  manufactured by Maxim: the MAX23x series chips.
  They incorporate a 5V to +-10V converter which works just fine.

2 Take the RS422 standard. It's a symmetric interface which uses two
  wires for each transmission line, but everything works with 5V.


Josef Moellers					| Nixdorf Computer AG
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