| 摘要 |
PURPOSE:To switch an incorporated ROM and an external ROM with a program on the ROM without loading the program onto a RAM, etc. CONSTITUTION:The same switching program are stored in the areas wherein the program is not switched by an I/O instruction in the incorporated ROM 33 and the external ROM 61, and whether an address inputted from a microprocessing unit(MPU) is in the area or not is decided by a first AND circuit 71 in a chip select(CS) control circuit 70. Then, any ROM of the incorporated ROM 33 or the external ROM 61 is selected by a second and a third AND circuits 72, 73 in accordance with a status signal separating the load/ unload of the external ROM 61 when the address is in the area. Further, any ROM of the incorporated ROM 33 or the external ROM 61 is selected by a fourth and a fifth AND circuits 74, 75 in accordance with the I/O instruction outputted from the MPU when the address is not in the area. |
