Using EXCP requires familiarity with the function and structure of the IOB, ECB, DCB, DEB, and optionally IOBE, DCBE,UCB and IEDB. DCB, IOB, IOBE, IEDB, and ECB fields are illustrated in the Control Block Fields section. The DEB fields used for EXCP and EXCPVR are illustrated in Control Blocks (all the DEB fields are illustrated in z/OS DFSMSdfp Diagnosis).

The IOB, ECB, DCB, and DEB must be in 24-bit virtual storage. The IOBE, IEDB, and DCBE may reside in 31-bit virtual storage, even if your program runs in 24-bit mode.

All EXCP control blocks that you provide must be located in storage that your program's protection key allows the program to modify. Descriptions of these control blocks follow.