mac os 9 Printer or Modem port connection

Hi all,
I have an app that is working through usb on OS X just fine. the app is written in Realbasic. i want the app to work with older macs running os 9 and that have no usb ports. i would like to use a mini-DIN-8 cable and need to know the wiring information like pin outs to the arduino board and any code that i have to write special for the arduino, like do i have to do anything special with pins 0 and 1, and what about power and ground etc.?
also if there are any realbasic users that have got a setup like this working what are the pitfalls to watch out for? also under os x the serial port speed is set at 57600 and is working fine. might this be a problem under os 9 with the modem or printer port? will i have to do anything special on the mac to get the communication going? which is a better port to use, printer of modem?
Jeff O’Brien

This is dredging up some old memories, but I seem to recall the printer and modem ports are nearly identical, but maybe TX and RX are swapped (DTE vs DCE?) between the two? They are RS422, not RS232, but wired in a certain configuration they are compatible with RS232 (422 is differential, and if TX- and RX- are tied to ground it behaves like 232 is my best recollection).

The Arduino USB and mini models have TTL level serial on pins 0 and 1, so you will need level translation to true RS232 levels/voltages (e.g. with a MAX232 or similar IC). You can't connect them directly. If you are building an interface circuit, it may be advantageous to use an RS422 interface IC (sorry, never done it, so I don't have part numbers off hand).

An Arduino serial would probably work as-is, although the combination of pseudo-RS232 support via transistors on one end and pseudo-RS232 by the RS422 port on the other end may be problematic.


i am using Arduino Decimilla. how would this effect your comments?

The Decimilla is a USB version, so the external rs232 (or 422) level/voltage translator circuit would be required.


i'm kinda new to this stuff. do you know of any tutorials or wiring diagrams/sample code for this type of connection? Jeff

Not off the top of my head. Here's an example device: the "RS232 serial programming adapter".

As often as this comes up (here and other places) I probably should go ahead and write a tutorial. I'll put that on my list of things to do. :)