Abstract: A data processing system includes a number of subsystems, all coupled in common to a system bus. Also coupled to the system bus is a hardware monitor interface unit (HMIU) for receiving all information transferred between subsystems. The HMIU includes programmable hit matrices (PHM's). The PHM's include memory circuits which generate "hit" signals when predetermined information addresses the memory circuits. The "hit" signals or binary ONE's are loaded into the memory circuits during a load mode during which system bus information specifically addressing the HMIU is received on two system bus cycles for each address location of the memory circuit. The data bus contains the memory circuit address during the first system bus cycle and the data during the second data bus cycle. An address bus signal identifies the cycle.