Vector lists supplying information to the application

All VTAM® application programs have access to vector lists that VTAM builds during its processing of the OPEN macroinstruction. These vector lists describe the features of VTAM to the application program and provide lists of resource identifiers that might be unknown to the application program.

Two address fields in the ACB point to the vector lists. These areas are located in storage that is read-only for the application program. The storage is addressable from the MVS™ address space or the VM virtual machine in which the OPEN is issued. Each address field contains the address of a vector list. The two vector lists are:

The access-method-support vector list (pointed to by the ACBAMSVL field in the ACB DSECT). This list describes the VTAM program that processed the OPEN macroinstruction.
The resource-information vector list (pointed to by the ACBRIVL field in the ACB DSECT). This list specifies resource identifiers and definition values that might be unknown to the application program.

OPEN processing vector lists built by VTAM have a field that is 1-byte in length. The format for vectors contained in the access-method-support vector list and the resource-information vector list is shown in Figure 1.

Figure 1. Format of vectors built by VTAM during OPEN processing

Diagram that describes the format of vectors built by VTAM during processing.

The vector lists can be examined at any time after the OPEN macroinstruction completes and until the CLOSE macroinstruction or equivalent terminations, such as an abend, occurs.