How do I synchronize two machines?

[JEC]

[edited from support email]

Here's what we'd like to have happen:

One DirectRT machine sends a TTL signal at the start of trial "n" and then continues with that trial. On that same trial on *another* machine, DirectRT sits waiting for that TTL signal. When it gets it, it continues with that trial. Consequently, both machines continue with the trial in near perfect synch.

Thus, we can present different images on different monitors to the same subject.

Can you describe the hardware end of it? e.g., the parallel to parallel connection required, port addresses, potential problems, and such?