Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.3 4.3bsd-beta 6/6/85; site l5.uucp
Path: utzoo!watmath!clyde!cbosgd!ihnp4!qantel!ptsfa!l5!gnu
From: gnu@l5.uucp (John Gilmore)
Newsgroups: net.micro.68k
Subject: Re: Altos 68000 - Random errors on HD1 - Fix
Message-ID: <75@l5.uucp>
Date: Sat, 7-Sep-85 14:54:10 EDT
Article-I.D.: l5.75
Posted: Sat Sep  7 14:54:10 1985
Date-Received: Mon, 9-Sep-85 02:01:20 EDT
References: <235@investor.UUCP>
Organization: Ell-Five [Consultants], San Francisco
Lines: 31
Summary: Terminating resistors go on the end of the cable.

In article <235@investor.UUCP>, rbp@investor.UUCP (Bob Peirce) writes:
>		     ...the instructions  said  to  remove  the
> termination resistor on drive 0 and said nothing about a resistor
> on drive 1.  None was installed at the factory.
>                                      ...Current thinking is  that
> there  must be a 220 ohm terminating resistor on drive 0 and a 1k
> ohm resistor on drive 1.

Terminating resistors are like the weight on the end of a rope, such
that when you snap the rope (run a wave down it), the wave doesn't
keep bouncing back and forth, but moves the weight a little (using up
energy) and damps it down.  Without them, the signals going to and from
the disk bounce back and forth in the cable and make noise that corrupts
the data.

They always go on the END of the cable.  If you have a cable that goes
from your controller to drive 0 and then to drive 1, put them on drive
1.  Note that most disks have TWO cables (plus power).  One cable goes
straight from the disk controller to the drive.  The other (typically
larger) goes to all the drives in series.  That's the one you have to
watch the termination on.

The actual value of the termination resistors depends on what's going on.
Traditional values are 220/330 ohms (220 between the cable and ground,
and 330 between the cable and +5 volts ... or maybe it's the other way).
These usually come as resistor paks (either a long skinny thing with little
wires dripping from it -- a "sip", or single inline package; or a chip-looking
object ("dip", dual inline package) often in a bright color like yellow).
There's usually a socket next to where the cable plugs in, where one of these
would fit (or is currently fitting).  It's not always obvious which way
the resistors plug in though.