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From: robin@uhccux.uhcc.Hawaii.Edu (Robin Amano)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Mac to IBM PC-AT cable
Keywords: Macintosh, IBM, cable
Message-ID: <9311@uhccux.uhcc.Hawaii.Edu>
Date: 11 Sep 90 00:44:57 GMT
References: <6368@jhunix.HCF.JHU.EDU>
Reply-To: robin@uhccux.UUCP (Robin Amano)
Organization: University of Hawaii
Lines: 59
Followup-To:

In article <6368@jhunix.HCF.JHU.EDU> hsu_wh@jhunix.HCF.JHU.EDU (William H Hsu) writes:

>     I am trying to solder up a cable to connect my IBM 286 AT
>clone (a CompuAdd 286-12, purchased in December of 1988) to a
>Macintosh SE.  By "connect" I mean that I would like to transfer
>text and other files modem-style between the computers (I have
>modems on both ends, but one is a 1200 baud and one a 2400, so
>I'd prefer to bypass them both) using only the telecom software
>on each machine.  I surmise that this requires a male mini DIN-8
>connector on the Mac end, but am not certain whether I have the
>I/O hardware on the AT end to support a "null modem" connection. 

The pins you need to use for the mac are:

1 = DTR
3 = TXD
4 = GND
5 = RXD

The male DB-9 on the AT clone is most likely a serial port and the pinout is:

1 = DCD
2 = RXD
3 = TXD
4 = DTR
5 = GND
6 = DSR
7 = RTS
8 = CTS
9 = RI

The cable should look like this:

                  AT Clone                      MAC

                  2 RXD ---------------------- 3 TXD
                  3 TXD ---------------------- 5 RXD
                  5 GND ---------------------- 4 GND

               |- 1 DCD ---------------------- 1 DTR
               |- 4 DTR
               |- 6 DSR
        
               |- 7 RTS
               |- 8 CTS


note pins 1,4, & 6 are jumpered together then connected to pin 1 of the mac.
also pins 7 & 8 are jumpered together but not connected to the mac.

Jameco sells Mac cables, but I'm not sure if they sell the kind you want.
You can check at:

Jameco Electronics
1355 Shoreway Road
Belmont, CA  94002
(415) 592-8097