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From: urlichs@smurf.sub.org (Matthias Urlichs)
Newsgroups: comp.periphs.scsi
Subject: Re: Gray vs Black termination plugs - what is the difference?
Message-ID: <hgkug2.eg5@smurf.sub.org>
Date: 9 Dec 90 17:59:51 GMT
References: <1990Dec6.153735.521@vixvax.mgi.com>
Organization: University of Karlsruhe, FRG
Lines: 20

In comp.periphs.scsi, article <1990Dec6.153735.521@vixvax.mgi.com>,
  keeney@vixvax.mgi.com (Richard Keeney) writes:
< I am looking for information on what is the difference between the
< standard gray colored SCSI terminator plug and the black SCSI terminator
< plug that Apple uses on the Macintosh IIFX.  So far, the best information
< I have is a guess that it has something to do with how the terminators are
< powered (i.e. no diode or something like that).  Exact technical details
< or a source of exact technical details would be appreciated.  
< 
The black terminators introduce some condensators to buffer the resistors'
power supply, which could be travelling from the Mac all the way through your
SCSI cable if no other device provides terminator power.

If the condensators aren't present, simultaneous changes on many lines
(data!) can cause glitches on other lines (notably REQ, which signal that the
data are ready).  At that point, however, they usually aren't --> big problem.

-- 
Matthias Urlichs -- urlichs@smurf.sub.org -- urlichs@smurf.ira.uka.de     /(o\
Humboldtstrasse 7 - 7500 Karlsruhe 1 - FRG -- +49+721+621127(0700-2330)   \o)/