Jenny Carillo at Yale was kind enough to provide us with her working MediaLab script which sends 'start' and 'stop' recording commands to a separate computer which interfaces with ASL's eye tracking system.
The two computers are connected with a special cable provided by ASL. If you're trying this at home, make certain you request ASL's specific 'auto record cable.'
The gist of the experiment is that a picture is displayed on the MediaLab screen for three seconds. Just before the image is shown, the eyetracker system starts recording. Just after the image is shown, the recording stopes.
You'll notice in the script that all 8 lines of the parallel port are turned on (255 decimal is equal to 11111111 in binary) while the recording is taking place. Then, they're set to zero to stop the data collection.
Thanks, Jenny!