The VTAM® application program places values in control blocks (ACB, EXLST, NIB, ASDP, and RPL) used by VTAM when the application program requests VTAM to perform actions on its behalf. When the request is accepted or completed, VTAM places values in the ACB, NIB, or the RPL control block as appropriate. The application program tests these values to determine the outcome of the request. This chapter discusses the ways in which the VTAM application program sets and tests these control block values.

Also discussed is certain VTAM information that is made available at assembly time in the form of macro global variables.