System Configuration : System Setup : Configuring Pro Tools Hardware Settings : Selecting Footswitch Control

Selecting Footswitch Control
(003 and 002 Only)
The footswitch connector on your 003 or 002 family interface lets you use a footswitch pedal to control either playback start/stop or recording punch in/out. Both QuickPunch audio punch-in and punch-out and MIDI punch-in and punch-out recording are supported.
Record Punch In/Out
Select this option to use a footswitch connected to your 003 or 002 family interface to punch in and punch out during recording.
Playback Start/Stop
Select this option to use a footswitch connected to your 003 or 002 family interface to start and stop playback.