Introduction

I decided some time ago to make my own adaptor cable so I could use my CM12 interface with my Macintosh.

Over time I made other adaptor cables for other serial devices as well as a complete replacement cable for the CM12 that was longer han the original and didn't require the adaptor stage.

During this time I discovered that there wasn't a really conclusive guide to how this was done. What was worse was the fact that some cables described elsewhere DIDN'T work.

Please enjoy!

The connectors

Serial (PC 9)

Also known as EIA/TIA 574

 (at the Computer)

9 PIN D-SUB MALE at the Computer.

Pin	Name	RS232	V.24	Dir	Description
1	CD	CF	109		Carrier Detect
2	RXD	BB	104		Receive Data
3	TXD	BA	103		Transmit Data
4	DTR	CD	108.2		Data Terminal Ready
5	GND	AB	102		System Ground
6	DSR	CC	107		Data Set Ready
7	RTS	CA	105		Request to Send
8	CTS	CB	106		Clear to Send
9	RI	CE	125		Ring Indicator

Note: Direction is DTE (Computer) relative DCE (Modem).
Note: RS232 column is RS232 circuit name.
Note: V.24 column is ITU-TSS V.24 circuit name.

Macintosh RS-422

It's possible to connect RS-232 peripheral to the RS-422 port available on Macintosh computers.

Use RXD- as RXD, TXD- as TXD, Ground RXD+, Leave TXD+ unconnected, GPi as CD.

 (at the computer)

8 PIN MINI-DIN FEMALE at the computer.

Pin	Name	Dir	Description
1	HSKo		Output Handshake
2	HSKi/CLK		Input Handshake or External Clock
3	TXD-		Transmit Data (-)
4	GND		Ground
5	RXD-		Receive Data (-)
6	TXD+		Transmit Data (+)
7	GPi		General Purpose Input
8	RXD+		Receive Data (+)

Note: Direction is DTE (Computer) relative DCE (Modem).

Note: GPi is connected to SCC Data Carrier Detect (or to Receive/Transmit Clock if the VIA1 SYNC signal is high). Not connected on the Macintosh Plus, Classic, Classic II, LC, LC II or IIsi.

Connection Table

Hints, Tips & Notes

Don't forget! The images here are from the FRONT of the plugs - when you are soldering (behind the plug) things will be back-to-front. Don't muddle your pins!

The pins on mini-DIN8 cables are very fine and can be fiddly to solder - make sure your soldering tip is fine. Extended soldering may cause the pins to move out of position - keep soldering times short or alternatively insert the plug in to an unused (spare) socket (not on your computer!) to keep them in position.

If you're not brave enough to try soldering a mini-DIN8 plug you can always salvage or buy a moulded one from somewhere. Use a multimeter / continuity tester to fing the right wire colour / pin combo. If you use a mini-DIN8 <-> mini-DIN8 serial cable you can cut it in half to make 2 adaptors / leads.

I find that the out sleeves on several mini-DIN8 plugs stop it from going in to the serial port properly (it strikes the case) - to prevent this I usually place a drop of glue or silicone in the sleeve when assembling the plug and pull the outermost section back about 5mm to allow better clearance.

Cable - I have made most of my cables from either flat modular 4 core telephone cable or the round 4 core variety to lengths of about 5m without any problems. If you require better signal immunity in high electrical noise environments (or have serial devices at high speeds) using a 4 cored shielded cable may be wise. I find it easiest to solder the braid / drain wire to the outer metal casing / rim of the plug at each end.

My crimper didn't accept RJ11 plugs - I found you could drive the pins down quite easily with a jeweller's screwdriver

Links

The Hardware Book - a great source of connector pinouts, adaptor cables and more

MouseHouse - the guide I originally used - this cable does NOT seem to work on ANY of my machines! See the note on the connection table above

Shed - The home of the ultimate Mac home automation application "Xtension" - also plenty more info there

Disclaimer

All information here is presented "as is" - no responsibility can be taken for use of this data in any way