Commodore A2232 Serial Expansion Board

The A2232 Multiport Serial Card is a standard 100-pin Zorro II expansion card for the Amiga (A2000, A3000, A4000). It provides the Amiga with 7 additional standard RS232 serial ports, capable of speeds from 50-19200 bps. For more serial channels, additional A2232 boards can be plugged into the system at the same time (up to five boards giving a total of 36 serial ports).

Hardware

The A2232 has its own MOS 65CE20 processor running at 3.58 Mhz and 16 kB of RAM (addressable by the Amiga's MC680x0) leaving the Amiga free for other tasks.

There are at least two revisions of the board:
Rev 4 boards have seven MOS Technology 6551 ACIA chips (Asynchronous Communications Interface Adapter)
Rev 6 boards have seven CSG (Commodore Semiconductor Group) 8551 ACIAs (HMOS-II variant of the 6551, released in 1984).

Silkscreen next to the Zorro connector says BERLIN/FISHER indicating the design was made by Creg Berlin and Terry Fisher.

The board originally came with user manual and seven 80 cm long adapter cables that provided the (then) standard DB25 connections.

Enhancements and modifications

Up to 57600 on all ports using a custom device and hardware modification: http://aminet.net/package/docs/hard/a2232tuning
Several sites also refer to mods for up to 115200 bps speeds (on all ports? Link?). Amiga.resource.cx also has a photo of a board with a title "Rev 6 board with RTS/CTS handshake mod". Another modification is to replace the 1.84 Mhz oscillator with a 3.68 Mhz one. This doubles the baud rates but the software won't know about this so the user must keep this in mind when using the board.

Connectors and pinouts

The connector nearest to the Zorro connector of the board (leftmost) is the first serial port.

The board uses seven mini 8-pin DIN connectors (similar to the S-Video or PS/2, but more pins) to fit all the connectors to the end plate of a single expansion board.
Image
Pinout:
1 = Rx
2 = Tx
3 = DSR
4 = CTS
5 = RTS
6 = DTR
7 = DCD
8 = GND

The pins 1 and 2 can be reversed on any port using jumpers
located on the jumperblock next to the connectors:

Image

Original cable pinout (8-pin mini DIN male -> 25-pin male)

8-pin mini DIN -> DB25
1 -> 3
2 -> 2
3 -> 6
4 -> 5
5 -> 4
6 -> 20
7 -> 8
8 -> 7
shell -> shell

If you need to build your own cables and you are using solderable mini din connectors, make sure it will fit deep enough into the socket when the board is inside the computer's case. A good source for molded connectors and cables are 8-pin Apple serial cables that have the same connector on both ends of the cable (and are fully connected). Cut one of those cables in half and you'll have a better-looking and mechanically more reliable connectors (not to mention that soldering those mini-din connectors is a real pain!). DB25 and DB9 connectors are still widely available.

If you only plan to build a single cable and use that with a modern machine thrue an USB-serial adapter (9-pin), you can build a null-modem included connection that plugs straight into the USB-adapter.

Alternative null-modem cable pinout (8-pin mini DIN male -> DB9 female)

8-pin mini DIN -> DB9
1 -> 3
2 -> 2
3 -> 4
4 -> 7
5 -> 8
6 -> 6
7 -> 1
8 -> 5

Editors notes: I had lot of problems finding a working pinout of the mini din connector. Commodore's system schematics does not indicate pin numbering and several sites indicated it other way around (looking at the male connector, not the female connector on the board). Finally when a friendly member of EAB forums provided me the measured pintouts I was able to build a working cable!

Usage

In Workbench the ports can be accessed using the serial.device driver (ver 33.11 from 1990 and newer, install disk available at Amiga.resource.cx) with the following unit numbers:

Unit 0 -> default port (set in Prefs serial panel)
Unit 1 -> Amiga's built-in port
Unit 2 -> A2232's port 1
Unit 3 -> A2232's port 2
Unit 4 -> A2232's port 3
Unit 5 -> A2232's port 4
Unit 6 -> A2232's port 5
Unit 7 -> A2232's port 6
Unit 8 -> A2232's port 7

If several A2232 boards are installed, the second board's unit numbers are 9-15 and so on. Up to five boards are supported (probably a limitation of the number of Zorro slots in any available machine).

In Amiga UNIX, the first port of the A2232 is known as /dev/term/ql00, second one ql01 and so on, thrue to ql06.

Probably the main selling point of the A2232 was the ability to connect several serial terminals to an AMIX machine. To start a login shell at any of the serial ports, use pmadm: pmadm -e -p serial -s ql00 This enables shell in the first port at the default speed of 9600 bps (defined as the 'serial' preset in /etc/screendefs). A real vintage dumb terminal (or a modern PC running terminal emulator, or a device like PockeTerm from Briel Computers) can be connected to the port and used to log into the machine.

Sources:
A2232 System schematics
http://amiga.resource.cx
http://www.l8r.net/technical/t-2232.shtml
Wikimedia Commons (mini 8-pin DIN diagram)
Thanks to mackbw on English Amiga Board for information on the pinouts!
Contributors to this page: MindWalker .
Page last modified on Saturday 29 of October, 2016 08:30:53 EDT by MindWalker. (Version 3)