I/O PCB

A PSB used in a DBCTL environment can contain any of these PCB types.

  • I/O PCB . In a CICS-DBCTL environment, an input/output PCB (I/O PCB) is needed to issue DBCTL service requests. Unlike other types of PCB, it is not defined with PSB generation. If the application program is using an I/O PCB, this has to be indicated in the PSB scheduling request, as explained in Format of a PSB.
  • Alternate TP PCB(s). An alternate TP PCB defines a logical terminal and can be used instead of the I/O PCB when it is necessary to direct a response to a terminal. Alternate TP PCBs appear in PSBs used in a CICS-DBCTL environment, but are used only in an IMS/VS DC or IMS TM environment. CICS® applications using DBCTL cannot successfully issue requests that specify an alternate TP PCB, an MSDB PCB, or a GSAM PCB, but PSBs that contain this kind of PCB can be scheduled successfully in a CICS-DBCTL environment. Alternate PCBs are included in the PCB address list returned to a call level application program. The existence of alternate PCBs in the PSB can affect the PCB number used in the PCB keyword in an EXEC DLI application program, depending on whether you are using CICS online, batch programs, or BMPs. For more information, see PCB summary.
  • DB PCB(s). A database PCB (DB PCB) is the PCB that defines an application program’s interface to a database. One DB PCB is needed for each database view used by the application program. It can be a full function PCB, or a DEDB PCB.
  • GSAM PCB(s). A GSAM PCB defines an application program’s interface for GSAM operations.

With DBCTL, a CICS online application program receives, by default, a DB PCB as the first PCB in the parameter list passed to it after scheduling.

With the EXEC DLI interface, in order to use system service requests, you specify the SYSSERVE keyword on the SCHD command to indicate that your application program can handle an I/O PCB. In an EXEC DLI environment, the SYSSERVE keyword does not change the PCB numbering, which means that your first PCB is still the DB PCB, and you do not need to specify a PCB number when you issue a system service request.

With the DL/I CALL interface, in order to use system service requests, you use the IOPCB parameter on the PCB to indicate that your application program can handle an I/O PCB. The I/O PCB will then be the first PCB in the parameter address list passed back to your application program.