Design requirements

Follow these procedures when writing this routine:

Consider the following restrictions when writing this routine:

The name of the SDDLU exit routine module should be ISTEXCSD; however, if you have written an alternate load module, use the load module name you assigned to your replacement module.
Do not issue any SVCs if this exit routine is running in SRB mode.
This exit routine should use only conditional storage invocations. You can reduce the possibility of a VTAM® abend during a storage shortage by coding conditional storage invocations.
Data is addressable in 31-bit mode only. Data is always presented with 31-bit addressability.
This exit routine can be above or below the 16M line.
This exit routine must be link-edited into the appropriate library. See Installing VTAM exit routines for more information.
Exit routines that perform I/O must be link-edited AMODE=31 and RMODE=24.
This exit routine runs under a VTAM subtask that permits the exit to perform any necessary I/O or other processing without affecting the VTAM main task.
Do not use VTAM macroinstructions in this routine.
This exit routine operates enabled in pageable storage. The routine gains control in supervisor state with a VTAM storage key. Errors in the routine could damage VTAM or system control blocks or modules.