From: tbc@netcom.com (Mike Garvey)
Newsgroups: comp.sys.apple2
Subject: Re: HELP: 9600bps modem won't work (2nd request)
Date: 19 Aug 92 05:11:21 GMT
Organization: Netcom - Online Communication Services (408 241-9760 guest)

In a prior missive, toddpw@cco.caltech.edu (Todd P. Whitesel) eloquently
scribed this stuff:

>In Greg Schaefer's ProTERM v3.0 manual, the suggested wiring for an Apple
>IIgs/IIc+ modem cable is (and it works -- I got ranges of 2690-3264 cps
>downloading textfiles from the Hayes BBS with an Intel 14.4ex): 
>
>Computer Port           Modem           Signal Name
>(Male MINI DIN-8)       (Male DB25)
>3                       2               TD (transmit data)
>5                       3               RD (receive data)
>4                       7               GND (signal ground)
>Short 8 to 4                            GND (signal ground)
>2                       5               CTS (clear to send)
>1                       4               RTS (ready to send)
>                        Short 4 to 20   DTR (data terminal ready)
>7                       8               DCD (data carrier detect)
>
>NOTE: This cable requires that "short circuits" be placed in the cable. This
>consists of creating a "Y" connection between the three pins. On the MINI
>DIN-8 end, pins 4 and 8 should be connected to each other as well as to pin 
>7 of the DB25. On the DB 25 end, pins 4 and 20 should be connected to each
>other as well as to pin 1 of the MINI DIN-8.

This cable will work fine on the Apple IIGS but there are two important
things to note. Shorting pin-8 and pin-4 of the DIN-8 to Signal Common (GND
[sic]) is supposed to dampen out excessive electrical noise as per standard
RS-422 to RS-232 conversion specs, which SHOULD result in more stable
connections, less dropouts, etc. In practice, the opposite is often true,
so if a user loses carrier frequently, he should consider removing the
short and just tie 4 to 7.

The only advantage of the DTR/RTS (4/20) short is if you wish to hangup the
phone by dropping the DTR line. In any case, you should configure the modem
to ignore the DTR signal (AT&D0, and/or a dip-switch) so the modem will
accept commands independent of the DTR state. Really ancient modems might
need a short between DTR/DSR (6/20) at the modem-end of the cable, in which
case you probably DON'T want to tie this to RTS.

The USRobotics modems are more flexible than most other high-speed modems
in that you DON'T have to support RTS as long you have a reasonably fast
computer (RTS traps for 'upload' overrun). You can then support DTR as
usual (i.e. hangup when DTR is lowered) in software.

Finally, a lot of Mac hardware handshaking cables DON'T support the DCD
(GPi) connection on pin-7 because not all Macs support it. These cables
will probably not be flexible enough to use with the GS and Apple II
software. One such cable, is the cable being shipped with the Supra
MacPack. Otherwise, it's identical to the above cable.

(Wanders off mumbling something about summary: buy a cable from InSync)

Be seeing you...
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Newsgroups: comp.sys.apple2