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From: kpc@enteract.com (Kevin Coffee)
Newsgroups: comp.sys.next.hardware
Subject: Modem Cables, Mac v Next serial, etc
Date: 16 Dec 1996 03:04:22 GMT
Organization: diffwerks
Lines: 48
Message-ID: <kpc-1512962106540001@beelzebub-47.d.enteract.com>
NNTP-Posting-Host: beelzebub-47.d.enteract.com

FWIW, and perhaps for clarity's sake...

According the the Guide to the Macintosh Family Hardware (p.360), which
covers a range of the 68K Mac models, that Macintosh hardware implements
RS-422. The serial pin-outs on both Mac serial ports are thus:

pin                 signal

 1                   DTR
 2                   CTS/TRC
 3                   TXD-
 4                   GND
 5                   RXD-
 6                   TXD+
 7                   GPi/DCD
 8                   RXD+

The Technical Introduction to the Macintosh Family, 2nd ed., notes that all
models "accept an input handshake signal (GPi) on their serial ports."
(p.317).

An empirical test of a hardware handshaking cable supplied with a "Mac"
modem (e.g. bundled with MacOS fax software), indicates the following pin
cross-connections:

DIN-8                 DB-25 -> which should rep

 1                     4            RTS
 2                     5            CTS
 3                     2            TXD
 4                     7            GND
 5                     3            RXD
 6                     -
 7                     -
 8                     7            GND


I would welcome further sampling/observations. This doesn't necessarily
apply to later DSP and/or PPC Mac machines (I think the Mac geoport may be
somewhat different).

Compare the above with man zs.

-Kevin


K e v i n  C o f f e e   /   d i f f w e r k s
<diffwerk@enteract.com> <kpc@enteract.com>