In addition to using an ACB, all VTAM® application programs can provide VTAM with a list of exit routines to use when external events occur that affect the application program. They can, for example, provide an error-handling exit routine for VTAM to schedule when a communication link between the application program and an LU is lost. When the event occurs, VTAM gives the exit routine control as soon as possible.

The following information shows two kinds of application program exit routines and a description of each.