【正文】 ntroller, however, In other words ,the other ponent are integrated into either the microcontroller or auxiliary circuits. These other ponents of the “puter” are data processing and storage devices, for example read only or random access memory containing the program to be executed, clocks and interfaces(serial or parallel). As a general rule ,a system based on a microcontroller therefore prises a microchip containing the microcontroller, and a plurality of microchips containing the external data processing and storage devices which are not integrated into the microcontroller. A microcontrollerbased system of this kind prises, for example, one or more printed circuit boards on which the microcontroller and the other ponents are mounted. It is the application program, I, e, the program which is executed by the microcontroller, which determines the overall operation of the microcontroller system. Each application program is therefore specific to a separate application. In most current application the application program is too large to be held in the microcontroller and is therefore stored in a memory external to the microcontroller, This program memory, which has only to be read , not written, is generally a reprogrammable read only memory(REPROM). After the application program has been programmed in memory and then started in order to be executed by the microcontroller, the microcontroller system may not function a expected. In the last unfavorable situation this is a minor dysfunction of the system and the microcontroller is still able to dialog with a test station via a serial or parallel interface, This test station is then able to determin the nature of the problem and indicates precisely the type of correction(software and physical) to be applied to the system foe it to operate correctly. Unfortunately, most dysfunctions of microcontrollerbased system result in a total system lockup, preventing any dialog with a test station. It is then impossible to determine the type of fault,i, it is a physical fault(in the microcontroller itself,in an external read only memory, in a peripheral device,on a bus,etc ) or a software fault( I,e. an error in the application program). The troubleshooting technique usually employed in these cases of total lockup is based on the use of sophisticated test devices requiring the application of probes to the pins of the various integrated circuits of the microcontrollerbased system under test. There are various problem associated with the use of such test devices for troubleshooting a microcontrollerbased system. The probes used in these test devices are very fragile, difficult to apply because of the small size of the circuit and their close packing,and may not make good contact with the circuit. Also, because of their high cost, these test devices are not mass produced. Consequently, faulty microcontrollerbased systems can not be repaired immediately, wherever they happen to be located a