Xref: utzoo news.sysadmin:2631 comp.unix.wizards:17852 Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!rutgers!aramis.rutgers.edu!geneva.rutgers.edu!hedrick From: hedrick@geneva.rutgers.edu (Charles Hedrick) Newsgroups: news.sysadmin,comp.unix.wizards Subject: Re: Preventing serial cable interference Keywords: serial cable interference Message-ID: Date: 27 Aug 89 00:49:11 GMT References: <33@octel.UUCP> <449@ctycal.UUCP> Organization: Rutgers Univ., New Brunswick, N.J. Lines: 18 The referenced article recommends a terminator that you can plug in when a line is open. That is a clean solution, but it's inconvenient, because users have to remember to plug in the terminator. Some kinds of terminals because unterminated when they are turned off. You may be able to get around this by installing terminating resistors permanently, probably in the machine room. We saw similar problems with open lines on a DEC-20 about 10 years ago. DEC field service whipped up an ECO for us using parts from Radio Shack. (It was thereafter known as "the Radio Shack ECO", and was dutifully installed by field service in all of our newer DEC-20's as they arrived.) I didn't look at the details, but I believe they did pretty much what was described here, except they used larger value resistors. They found a value that provided enough termination to prevent open lines from ringing, but didn't interfere with normal communications when something was plugged in. I don't know what value they used. Presumably somewhere between 10K and 100K. You might experiment.