PERCON is executable in both 24- and 31-bit addressing modes. 31-bit addressing should be used if virtual memory requirements are correspondingly high (> 16 Mbytes) and PERCON is to be called as a subprogram or user modules are to be connected.
When called autonomously PERCON executes in 24-bit addressing mode unless otherwise specified. If 31-bit addressing mode is to be activated, PERCON must be started with /START-PERCON PROGRAM-MODE=ANY.
If PERCON is called as a subprogram and if the linking loader module PCROOT (LLM) linked to the main program (see "Calling PERCON as a subprogram ") has to change addressing mode (for instance, because PERCON has been loaded into the upper address space as a subprogram), the old addressing mode is reinstated when the user returns to the main program.
The following points must be borne in mind with regard to user interfaces:
PERCON does not change the addressing mode when calling a user interface.If PERCON and the user interface have different addressing modes:
the user interface must be adapted to have the same addressing mode as PERCON, or
if this is not possible, a “GLUE program” must be inserted in order to standardize the addressing mode.
Irrespective of the addressing mode, PERCON uses the 31-bit system interface (PARMOD=31). For this reason a 31-bit file control block (FCB) is offered for label processing in the case of user interfaces.