| 摘要 |
PURPOSE:To prevent the runaway of a microcomputer due to the break of an external power supply of a microcomputer system using an external memory by providing a specific instruction code generator to the microcomputer system together with a starting gate for said code generator. CONSTITUTION:An instruction generator 12 sends a code of Yen39 to a data bus when a power supply is cut after an operation code is fetched and as long as an instruction belongs to an external memory 21. Thus an MPU 11 fetches mistakenly said code as an operand and therefore the MPU 11 judges an instruction of Yen3,939 and jumps to Yen3,939 in case the memory 21 uses an absolute address jump instruction. However the MPU 11 has runaway if the absolute address is not allocated to the memory 21. In this respect, the memory 21 uses only a relative address jump instruction so that the memory 21 does not get out of its space. |
