RS-422 is basically just higher-speed RS-232. It can be programmed just like RS-232 for basic serial communication.
The two big differences are in speed, and speed control. A 16550 UART on the PC side provides a 115,000 bps serial connection over RS-232. The RS-422 on a Mac is capable of double that, 230,000 bps, natively. However, the port can be 'externally clocked', so that a device can increase the clock even above that. Apple's serial networking protocol, "LocalTalk" could be externally clocked up to 2 Mbps!

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Basically what I would like to do is hook up a controller or interface board to the Mac much in the same way that they have boards for the PC. These boards usually will take standard analog or digital inputs and they in turn have an output bus in which you can turn on/off relays. That is pretty much the extent of it. These boards though are PC based and use RS-232...so if RS-422 is compatible then I assume that all that would be needed is an adapter cable, correct?

I usually use BASIC to access the port.

In essence I would be treating the Macintosh as a monstrous "Basic Stamp". The major differences is that I have many more programs at my fingertips and I could write HUGE programs.

So that also goes without saying that I need a version of Basic that will run on the Mac and still be able to access that serial port.

Is that a can do?

Thanx,

Geo