The command parameter structure
The command parameter structure consists of a series of addresses. The first address points to the EXEC interface descriptor (EID), which consists of a bit string that describes the type of request and identifies each keyword specified with the request.
The remaining addresses point to pieces of data associated with the request; for instance, the second address always points to the program name. You can examine the parameters in the list to determine the values of the keywords. You can also modify values of parameters specified on the request. For example, you could change the name of the program involved in the request, or add the SYSID to route the link request to a remote system.
End of parameter list indicator
The high-order bit is set on in the last address set in the parameter list to indicate that it is the last one in the list. On return from your user exit program, CICS scans the parameter list for the high-order bit to find the last parameter. Therefore, if you modify the length of the parameter list, you must also reset the high-order bit to indicate which is the new last address.
For example, if the parameter list specifies only the first two addresses (PC_ADDR0, the address of the EID, and PC_ADDR1, the address of the name of the program named in the link request), the high-order bit is set on in PC_ADDR1. If you extend the parameter list by setting the address of a SYSID in PC_ADDR7, you must unset the high-order bit in PC_ADDR1 and set it on in PC_ADDR7 instead.
The original parameter list, as it was before XPCREQ was invoked, is restored after the completion of XPCREQC. It follows that EDF will display the original command before and after execution: EDF will not display any changes made by the exit.