The application program can supply VTAM® with special-purpose exit routines to handle error situations. These are the LERAD and SYNAD exit routines. In addition, the application program can supply VTAM with a TPEND exit routine that is called when VTAM is forced to close down.

The LERAD or SYNAD exit (usually the LERAD) is scheduled by VTAM when an APPCCMD has a general return code higher than 0. VTAM interrupts whatever part of the application program is executing when the error is discovered (including another exit routine) and schedules the exit. The exit is responsible for setting register 15 and register 0 before the application program again receives control.

The LERAD and SYNAD exits might be called after the application program has already processed an error. Much of the error feedback information in the RPL is available when the RPL is checked prior to being cleared and marked as inactive. For example, if an APPCCMD request specifies an RPL exit, error feedback information is available to the RPL exit. Even if the exit takes recovery action, the LERAD or SYNAD is still scheduled for error situations and is driven after the RPL exit completes and the APPCCMD is considered complete.

If no LERAD or SYNAD exit routine is provided, register 15 and register 0 are set to the general return code and recovery action return code, respectively. If LERAD or SYNAD is entered, register 0 contains the recovery action return code.

For more information on these exits, refer to z/OS Communications Server: SNA Programming and Using exit routines in this book.