Emulating a Motorola CDX268 terminal on a Macintosh or Apple II is easy. The
CDX286 is what was once, affectionately, called a "glass TTY". It's a very
basic terminal that you can configure for baud rate, data and stop bits, and
parity. The port can be configured for either RS-232 or RS-422. It requires no
strange or out-of-the-ordinary protocols. All of this means that almost any
terminal emulation program for the Macintosh or Apple II can be set up to act
like a CDX268.
To do the emulation, set it up CDX286 in TTy mode and connect the appropriate
cable to the built-in serial port. The cable, like your configuration, depends
on what you're connecting to.