The ACB contains the following information that describes the application program to VTAM®:

• The name of the access method used in operating the ACB (VTAM).
• The address of an application program identifier. The application program identifier must match the name that is specified on the APPL definition statement provided as part of the VTAM definition. When the application program opens an ACB, VTAM verifies that the ACB name is defined to VTAM. If the name is not defined, VTAM does not process the ACB.

  If an application program name is not specified on the APPLID operand of the ACB macroinstruction, VTAM uses a name supplied by the operating system. If the name supplied by the operating system does not match a name on the APPL definition statement, VTAM does not process the ACB. The following indicate what name is used for each operating system:

  If the application program is started by a job step that is a procedure invocation, the name is the procedure step name in the job control language (JCL) for the application program. Otherwise, it is the job step name in the JCL.

• Optionally, the address of a password associated with the application program. When an ACB is opened, VTAM compares the ACB password with a password that is defined on the APPL definition statement. If the passwords do not match, VTAM does not process the OPEN macroinstruction. If a password is not specified on the APPL statement, you do not need to specify a password on the ACB macroinstruction.
• The address of an exit list (EXLST control block) containing the names of exit routines written in the VTAM application program to handle specific events. These are described in detail in Using exit routines.
• An indication of whether the application program accepts sessions that it has not initiated (MACRF=LOGON). If MACRF=NLOGON is specified, an application must use OPNDST OPTCD=ACQUIRE to establish sessions.

  If the application program is to establish sessions in which it acts as the SLU, you must code MACRF=LOGON.

• An NIB, if the application program is an authorized CNM application program, to establish access to an SSCP-LU session between the SSCP and the application program.
• Indicates whether the application program supports LU 6.2 architecture protocol extensions for full-duplex and expedited data transmission.
• An indication of whether the application program is capable of persistent LU-LU session support.
• An indication of whether the OPEN associated with this ACB is to be considered a multinode persistent sessions forced takeover request.
• An indication of whether the application program is authorized to use the performance monitor interface.
• A 4-byte field set by the application program to provide the address of the Application-ACB vector list.
• A 4-byte field that can be set by the application program and used for any application program purpose. VTAM ignores this field. For example, the field can be set with the address of a control block to be used by the application program when an exit routine is invoked.
• A 4-byte field containing the address of the access-method support vector list. During the OPEN processing, VTAM fills in this field. The vector list contains the release-level, component-identification, and function-list vectors and is described in The access-method-support vector list.
• A 4-byte field containing the address of the resource-information vector list. During the OPEN processing, VTAM fills in this field. The vector list contains information about the application program that opened the ACB and is described in Resource-information vector list.

The following sample ACB macroinstruction is used to build an access method control block:

ACB1     ACB   AM=VTAM,APPLID=APID1,                                   C
               PASSWD=PSWD1,EXLST=EXIT,MACRF=LOGON,                    C
               PARMS=(USERFLD=A(MYLU))
         .
         .
         .
APID1    DC    AL1(L'AP1NAME)
AP1NAME  DC    C'MYPROG'
PSWD1    DC    AL1(L'PASSCHAR)
PASSCHAR DC    C'JOE007'
EXIT     EXLST AM=VTAM,NSEXIT=NSRTN,SCIP=SESSCTL,                      C
               LOGON=CINIT,                                            C
               LOSTERM=LTRTN
MYLU     DS    XL100

• ACB1, the symbolic name for this ACB, is included in the OPEN macroinstruction that is used to open this ACB.
• AM=VTAM identifies VTAM as the access method for this ACB.
• APID1 is the address of the application program identification (MYPROG). A request to initiate a session with this application program can specify MYPROG.
• MYLU is a control block to be associated with the ACB. It might contain the status flags and other variables associated with the application program LU.
• PSWD1 is the address of the password (JOE007).
• EXIT is the name of the exit list created by the EXLST macroinstruction.
• MACRF=LOGON specifies that:
  • Other LUs can initiate a session with this application program
  • VTAM schedules the SCIP exit routine when a BIND request is received by the application program.