Instructions that add and remove a linkage stack entry

The three instructions that cause the system to add or remove entries on the linkage stack are:

The stacking program call (PC), which adds an entry when it passes control to another routine.
The branch and stack (BAKR), which adds an entry whether it branches to another routine or not.
The program return (PR), which removes an entry when it returns from a call or branch made with either a stacking PC or a BAKR.

This section introduces each instruction and gives simple examples of each. It is not intended to direct you in your coding. For complete descriptions of the instructions, see Principles of Operation.

The stacking PC instruction adds an entry to the linkage stack. Synchronous cross memory communication describes the two types of PC linkages. The stacking PC uses the linkage stack to save the user's environment. The basic PC, on the other hand, requires that the PC routine provide code to save the user's environment. The stacking and basic PC instructions are cross memory instructions; they are described in more detail in PC linkages. Synchronous cross memory communication also contains a comparison of the coding of a stacking PC and a basic PC. The linkage stack instructions BAKR and PR are described in the following sections.