Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 (Fortune) 6/7/84; site dmsd.UUCP Path: utzoo!linus!decvax!decwrl!amd!fortune!hpda!dmsd!bass From: bass@dmsd.UUCP (John Bass) Newsgroups: net.periphs Subject: Re: How long can an RS232 line be? Message-ID: <150@dmsd.UUCP> Date: Tue, 16-Oct-84 01:15:05 EDT Article-I.D.: dmsd.150 Posted: Tue Oct 16 01:15:05 1984 Date-Received: Thu, 18-Oct-84 19:24:23 EDT References: <487@oddjob.UChicago.UUCP> Lines: 24 At SRI in the late 70's we ran some 2000-3000 ft lines running at 2400/4800 baud with little trouble. Some would work at 9600. The lines were 2 twisted pairs with foil shield. Some terminals had "marginal" rs232 drivers/receivers and worked better after using different chips. Looking at the signals at the computer end the receiver waveforms were nearly sine waves. Some of the installations also showed 4-15v of 60hz noise ... much of that was ground noise ... both earth ground variances and inductive pickup from the lines running along side power lines. I have heard that some folks have used an RC filter to waveshape the signal and cut out some of the 60hz noise ... but don't know what was used. The biggest problems were caused by lines talking to themselves when a remote terminal was powered off. The floating end of a 2000ft twisted pair lines passes back all sorts of garbage into the receiver on the computer end. The logon banner would couple back into the receiver, echo/getty/login output from the input would keep the line talking for hours on end. A resistive termination to ground at the terminal end helped on some lines. Some lines had repeated driver/receiver failure ... ground differential? inductive kicks? Have fun .. John Bass