IPCS gives an MPF exit routine control from the format model processor service after a line of output has been formatted, but before it is printed. IPCS passes control to the MPF exit once for every line of output when the initiating exit program sets the option bit ADPLPOLM on, and places the address of the MPF exit routine in ADPLPLME.

IPCS also passes control to the MPF exit routine when a model entry with the CALLRTN flag set on is processed. An additional call is made to the MPF exit after the model processor has finished. The MPF exit sets a bit in the FXL, FXLLAST, to indicate this special call took place.