Macintosh Plus: Modem 300 & Modem 1200 cable pinouts


Below is the wiring diagram of the connection between a Macintosh Plus and
an Apple Modem 300 & 1200. Cables 1 and 2 may be used together for the
connection or a custom cable 3 may be constructed.
CABLE 1
Macintosh Modem Cable
590-0197

Macintosh Apple Modem
Connector Connector
(DB-9) (DB-9)

Comments Signal Pin Pin Signal Comments
Name Name

Chassis,frame Ground GND 1 <-+-> 8 GND Chassis,Frame Ground
|
Signal Ground SGND 3 <-+-> 3 SGND Signal Ground
Output; Transmit Data TXD 5 <---> 9 RCD Input; Receive Data
12-Volt Line 6 <---> 6 DTR
Output; Ready to Send RTS 7 <---> 7 DCD Input; Data Carrier Detect
Input; Receive Data RCD 9 <---> 5 TXD Output; Transmit Data

NOTE: There are many variations on connecting pins 1, 3 and 8, but the basic
intent is to bring all three of those pins to ground on the Mac side.
Connect Signal Ground to Chassis Ground if you want a slightly better
noise margin.

CABLE 2
Macintosh Plus Circular 8 to DB-9 Adapter
699-0372

Circular 8 Signal DB-9
1 HSKo (+12V) 6
2 HSKi 7
3 TXD- 5
4 GND 3*
5 RXD- 9
6 TXD+ 4
7 No Wire
8 RXD+ 8
GND 1*

* Pins 1 and 3 on the DB-9 end are jumpered together.

The pins on the male end of the circular 8 connector are numbered as shown:

6 7 8
3 4 5
1 2

CABLE 3

Macintosh Plus Circular 8 to DB-9 Custom Cable

Circular 8 DB-9
1 HSKo (+12V) 6 DTR
2 HSKi 7 DCD
3 TXD- 9 RCD
4 GND 3,8 SGND,GND
5 RXD- 5 TXD
6 TXD+ No Wire
7 No Wire No Wire
8 RXD+ 8 GND


Published Date: Feb 19, 2012