Newsgroups: comp.sys.ibm.pc.hardware
Path: utzoo!telly!robohack!druid!darcy
From: darcy@druid.uucp (D'Arcy J.M. Cain)
Subject: Re: Serial-port connections
Message-ID: <1990Aug13.151314.26724@druid.uucp>
Organization: D'Arcy Cain Consulting, West Hill, Ontario
References: <54123@iuvax.cs.indiana.edu>
Date: Mon, 13 Aug 90 15:13:14 GMT

In article <54123@iuvax.cs.indiana.edu> bobmon@iuvax.cs.indiana.edu (RAMontante) writes:
>"How long is a serial port?" Or, more accurately...my cousin has a dumb
>device with a serial port (connected to some relays), and he'd like to
>control the device remotely from his P.C.  My question is, how far can
>the remote device be from the the P.C., and how should it be connected?
>Would a "null modem" cable be reliable over a 200-foot span?  If not,
>what's the cheapest connection?  We thought of two modems and some phone
>wire; would the phone wire need to be powered then?  (300-baud would be
>good enough; it's not a high-speed device out there.)

The RS-232-C standard specifies that a 50' cable should be capable of handling
up to 19200 BPS (loosly meaning 19200 baud) but most hardware today can handle
longer distances.  In general, as you lower the baud rate, the maximum safe
length increases.  Do some testing to find a baud rate that works reliably
then cut that in half for a margin of safety.  I am sure that you will be
able to do better than 300 baud.

-- 
D'Arcy J.M. Cain (darcy@druid)     |
D'Arcy Cain Consulting             |   MS-DOS:  The Andrew Dice Clay
West Hill, Ontario, Canada         |   of operating systems.
+ 416 281 6094                     |