Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!shadooby!samsung!uunet!portal!cup.portal.com!mmm
From: mmm@cup.portal.com (Mark Robert Thorson)
Newsgroups: sci.electronics
Subject: Re: Transmission Lines - What Are They??
Message-ID: <24023@cup.portal.com>
Date: 13 Nov 89 22:27:19 GMT
References: <868@encad.Wichita.NCR.COM> <1989Nov12.013850.7756@utzoo.uucp>
  <1989Nov12.043426.11834@utzoo.uucp>
Organization: The Portal System (TM)
Lines: 16

A good cookbook rule for TTL is:

1)  Series termination -- 10 to 100 ohms placed right near the driver.  I.e.
    the driver feeds the resistor, and the rest of the circuit is fed from
    the other side of the resistor.

2)  Parallel termination -- 220 ohms to Vcc and 330 ohms to ground, placed
    at the far end from the driver.  The signal line should be "serialized",
    i.e. any forks or loops should be removed so that it doesn't have any
    long stubs between the driver and the terminating resistors.  For a line
    with many loads, you may wish to put drivers in parallel.  If you do,
    use drivers in the same package to minimize skew caused by temperature
    differences.

If you need better numbers than these, substitute values while viewing the
signals on a scope.