The service provider must also supply the user with a PC number. The service provider creates this number by concatenating the LX to the entry table index (EX). As previously stated, the LX is an index into the linkage table. The EX is an index into the entry table and identifies the relative entry in the entry table that corresponds to the PC routine that is to receive control. Example: If the first table entry corresponded to the PC routine, the EX would be X‘00’; if it was the second entry, the EX would be X‘01’, and so forth. The service provider is responsible for calculating and keeping track of entry table indexes. When a program issues the PC instruction, the system uses the PC number to locate the correct entry table entry and transfer control to the PC routine.

The service provider and the user must agree on a method the service provider will use to provide the user with the PC number. The service provider might, for example, supply a macro that returns the PC number to the user. Or the service provider could place the PC number in a storage area common to both the service provider and the user. The user could then retrieve the PC number from the common area.

In addition, when you use a reusable LX, the service provider and the user must also agree on a method the service provider will use to provide the user with the LX sequence number. The service provider could, for example, supply a macro that returns the PC number/LX sequence number to the user. Or the service provider could place the PC number/LX sequence number in a storage area that is common to both the service provider and the user. The user would then retrieve the PC and LX sequence number from the common area.