The first time you issue a SPIE macro during the performance of a task, the system creates a program interruption element (PIE) in the virtual storage area assigned to your job step. The system also creates a PIE whenever you issue a SPIE macro and no PIE exists. For the format of the PIE, see z/OS MVS Data Areas in the z/OS Internet library.
The PICA address in the PIE is the address of the program interruption
control area used in the last execution of the SPIE macro for the
task. When control is passed to the routine indicated in the PICA,
the 
ESA/390
(basic control) mode old program
status word contains the interruption code in bits 16-31 (the first
byte is the exception extension code and the second is the exception
code); you can test these bits to determine the cause of the program
interruption. See z/Architecture® Principles
of Operations SA22–7832 for an explanation of the format
of the old program status word. The system stores the
contents of registers 14, 15, 0, 1, and 2 at the time of the interruption
as indicated.