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From: mmm@cup.portal.com (Mark Robert Thorson)
Newsgroups: sci.electronics
Subject: Re: Transmission Lines - What Are They??
Message-ID: <24187@cup.portal.com>
Date: 18 Nov 89 17:34:31 GMT
Article-I.D.: cup.24187
References: <868@encad.Wichita.NCR.COM> <1989Nov12.013850.7756@utzoo.uucp>
  <24023@cup.portal.com> <46e0fd1a.1fbc0@chanel.UUCP>
Organization: The Portal System (TM)
Lines: 19

ngc@chanel.UUCP (Chris Ng) says:

> In article <24023@cup.portal.com>, mmm@cup.portal.com (Mark Robert Thorson) wri
> tes:
> > A good cookbook rule for TTL is:
> > 1)  Series termination -- 10 to 100 ohms placed right near the driver.  I.e.
> > 
> > 2)  Parallel termination -- 220 ohms to Vcc and 330 ohms to ground, placed
> 
> Parallel termination draws current constantly while
> series termination does not. May be it doesn't matter in your design,
> just a side note.

Another cookbook rule:  use series termination where short lines with few
loads are being drived, such as a microprocessor driving a few peripheral
and memory chips, or an address multiplexer driving a bank of DRAM chips.

Use parallel termination where the line is long and has many loads, like
a system clock line that snakes all over your board.