The programmed communication control unit (PCCU) definition statement identifies the communication controller where the NCP is loaded. It is required in VTAM® systems and defines the VTAM functions that are provided for this NCP. Code at least one PCCU definition statement for each NCP.

Sample PCCU definition statement

Following is a sample PCCU definition statement:

PCCU116  PCCU  AUTODMP=NO,            AUTOMATIC DUMP OPTION
               AUTOIPL=NO,            AUTOMATIC RE-IPL OPTION
               AUTOSYN=YES,           SYNCHRONIZE WITH ACTIVE NCP
               CUADDR=016,            3745 IPL ADDRESS
               LOADFROM=EXTERNAL,     LOAD 3745 FROM 3745 DISK
               DUMPLD=YES,            DUMPLOAD USING 3745/3720 DISK
               DUMPDS=NCPDUMP,        NCP DUMP DATA SET DDNAME
               MDUMPDS=MOSSDUMP,      MOSS DUMP DATA SET DDNAME
               CDUMPDS=CSPDUMP,       CSP  DUMP DATA SET DDNAME
               MAXDATA=5000,          MAXIMUM PIU SIZE
               NETID=USIBMCSS,        NETWORK IDENTIFIER
               VFYLM=YES,             NOTIFY OPERATOR IF WRONG LOAD MODULE
               VFYC=YES,              VERIFY LOAD MODULE AND RRT MATCH
               ⋮
               SUBAREA=116            OWNING SSCP SUBAREA

SUBAREA operand

The SUBAREA operand associates the communication controller with a VTAM host when the NCP is activated. If each host provides the same function for the NCP, only one PCCU definition statement is necessary, but the operator might need to override unique attachment requirements.

Multiple PCCU definition statements

If you code multiple PCCU definition statements, VTAM compares its network identifier and subarea number to the values of the NETID and SUBAREA operands on all the PCCU definition statements to locate the one that applies to it. However, VTAM selects this PCCU definition statement in the following order:

1. The VTAM host processes the first PCCU definition statement whose NETID and SUBAREA operands match those in VTAM.
2. If no such PCCU definition statement exists, the VTAM host processes the first one that has the same NETID as VTAM and that does not have a SUBAREA.
3. If a PCCU definition statement as described in step 1 or 2 does not exist, the VTAM host processes the first PCCU definition statement without a NETID operand but with a SUBAREA value equal to that found in VTAM.
4. Finally, if a PCCU definition statement as described in step 1, 2, or 3 does not exist, the VTAM host processes the first PCCU statement for which neither the NETID nor SUBAREA operand is coded.

The NCP for an IBM® 3745 or 3720 Communication Controller can be loaded from either of the following locations:

• The NCP load library at the host (LOADFROM=HOST)
• The 3745 or 3720 disk (LOADFROM=EXTERNAL)

When the VARY ACT command is issued to activate NCP, the LOADFROM operand on the PCCU definition statement is used if the LOADFROM operand is not specified on the VARY ACT command.

Automatic dump and reload

The AUTODMP and AUTOIPL operands on the PCCU definition statement inform VTAM whether to automatically dump and reload the NCP if an error is encountered. To have an IBM 3745 or 3720 Communication Controller dump and reload the NCP from its disk, do one of the following actions:

• Code the DUMPLD=YES operand on the PCCU definition statement.
• Specify the DUMPLOAD=YES operand on the VARY ACT command.

These operands are then ignored if the operation is successful. The NCP dump can then be transmitted to the VTAM host from the communication controller disk at a later time.

If the communication controller is a 3725 or the dump is not stored on the communication controller disk, it is transmitted to the VTAM host and stored in the file identified by the DUMPDS operand on the PCCU definition statement. If you specify the CDUMPDS and MDUMPDS operands on the PCCU definition statement, they identify the files in which a CSP and a MOSS dump, respectively, are to be stored in the VTAM host. If you do not specify these operands, the corresponding dump is stored in the file identified by the DUMPDS operand.

Verifying the load module

When you load the NCP, you can use the AUTOSYN operand of the PCCU definition statement to request VTAM to compare the name of the load module currently in the communication controller to the NEWNAME operand on the BUILD definition statement. If you code AUTOSYN=YES, VTAM uses the current NCP load module; if you code AUTOSYN=NO, the operator must determine whether the communication controller should be reloaded with a new copy of the NCP. If the NCP load module and the NEWNAME operand do not match, the VFYLM operand determines whether the operator is to be informed of the mismatch (VFYLM=YES) or whether the operator must reload the communication controller with the different load module (VFYLM=NO).

For a channel-attached NCP, the CUADDR operand of the PCCU definition statement indicates the channel unit address of the communication controller that VTAM should use to load the NCP.

Verifying time stamps

When the NCP/EP definition facility (NDF) is used to generate NCP, a resource resolution table (RRT) is created in addition to the NCP load module. At initialization, VTAM reads the RRT to determine what resources are contained in the NCP load module. VTAM examines the time stamp of the RRT and verifies that it corresponds to the NCP load module associated with the RRT.

The VFYC operand on the PCCU definition statement enables you to specify what action VTAM should take if the time stamps do not match. If you code VFYC=NO or allow it to default and VTAM detects a correlator mismatch, VTAM sends a message to the operator explaining that the NCP is being loaded because of the mismatch. If you specify VFYC=IGNORE, VTAM continues the NCP activation process regardless of the time stamps of the NCP load module and the RRT; no message is issued.