Support for HPDT is exchanged between an application and VTAM® when the application opens its ACB.

VTAM informs an application about its level of support for HPDT on the LU-6.2-support-function-list vector, which is located in the access-method-support vector list. The application must examine this vector list to determine if the VTAM with which it has opened its ACB supports HPDT. For more information about using vectors and vector lists, see Access-method-support vector list.

Determining VTAM's support for HPDT can also be performed at assembly time by referencing the &ISTGA56 variable on the ISTGAPPC macroinstruction. Refer to z/OS Communications Server: SNA Programmer's LU 6.2 Reference for more information.

Applications inform VTAM about their intent to use the HPDT interface on the application-capabilities vector. For more information about this vector, see Vector lists supplying information to VTAM.