... but I think Jorge wants to have "wrapper" functions for the routines provided by the monitor.

This might perhaps consist of simply remapping of the input/output variables from Keil's standard to PaulMon's and calling (jumping) to the appropriate PaulMon's vector. The description of how Keil allocates registers to the input/output variables of the functions can be found in the doc.

AFAIK, Keil uses the "caller saves" convention, so that the routine can spoil the registers, including acc, b and dptr (but I might be wrong - Keil fans can correct me).

JW