The logon-interpret routine is run synchronously in pageable storage under the control of VTAM®, not under the control of an application program. For the application program to receive the logon, this routine must validate the logon, obtain the symbolic name of the application program to receive control, and provide this name to VTAM. Otherwise, the routine specifies that the logon is not valid or that the name of the application program was not found.

Because the logon-interpret routine operates at VTAM's main task dispatching priority, there is a possibility of lockout if a wait requires another task action. The routine gets control in supervisor state with a VTAM storage key, so errors within the routine could cause damage to VTAM or to system control blocks and modules.