Program communication block (PCB) lists
In your application program, code your PCB or GPSB list in the following format.
PCB list format
[IOPCB]
[Alternate PCB ... Alternate PCB]
[DB PCB ... DB PCB]
[GSAM PCB ... GSAM PCB]
Each PSB must contain at least one PCB. An I/O PCB is required for most system service calls. An I/O PCB or alternate PCB is required for transaction management calls. (Alternate PCBs can exist in IMS™ TM.) DB PCBs for DL/I databases are used only with the IMS Database Manager under DBCTL. GSAM PCBs can be used with DCCTL.
Format of a GPSB PCB list
[IOPCB]
[Alternate PCB]
A GPSB contains only an I/O PCB and one modifiable alternate PCB. (A modifiable alternate PCB enables you to change the destination of the alternate PCB while the program is running.) A GPSB can be used by all transaction management application programs, and permits access to the specified PCBs without the need for a specific PSB for the application program.
The PCBs in a GPSB have predefined PCB names. The name of the I/O PCB is IOPCB. The name of the alternate PCB is TPPCB1bb. The minimum size of the I/O work area that IMS generates for GPSBs in a DBCTL environment is 600 bytes.
PCB summary
- DB Batch Programs
- If CMPAT=Y is specified in PSBGEN, the I/O PCB is present in the PCB list; otherwise, the I/O PCB is not present, and the program cannot issue system service calls. Alternate PCBs are always included in the list of PCBs that IMS supplies to the program.
- BMPs, MPPs, and IFPs
- The I/O PCB and alternate PCBs are always passed to BMPs, MPPs,
and IFPs.
The PCB list always contains the address of the I/O PCB, followed by the addresses of any alternate PCBs, followed by the addresses of the DB PCBs.
- CICS® Online Programs with DBCTL
- If you specify the IOPCB option on the PCB call,
the first PCB address in your PCB list is the I/O PCB, followed by
any alternate PCBs, followed by the addresses of the DB PCBs.
If you do not specify the I/O PCB option, the first PCB address in your PCB list points to the first DB PCB.
The following table summarizes the I/O PCB and alternate PCB information.
Environment | CALL DL/I | |
---|---|---|
I/O PCB address in PCB list | Alternate PCB address in PCB list | |
MPP | Yes | Yes |
IFP | Yes | Yes |
BMP | Yes | Yes |
DB Batch1 | No | Yes |
DB Batch2 | Yes | Yes |
TM Batch3 | Yes | Yes |
CICS DBCTL4 | No | No |
CICS DBCTL5 | Yes | Yes |
- CMPAT = N specified.
- CMPAT = Y specified.
- CMPAT = Option. Default is always to Y, even when CMPAT = N is specified.
- SCHD request issued without the IOPCB or SYSSERVE option.
- SCHD request issued with the IOPCB or SYSSERVE for a CICS DBCTL request or for a function-shipped request which is satisfied by a CICS system using DBCTL.