| 摘要 |
PURPOSE:To alter one part of mask ROM data by providing a P-ROM, and reading the data from the P-ROM instead of from the mask ROM in a range designated with an address. CONSTITUTION:When the data of a mask ROM 1 are to be altered, a mode signal is set at a low level, and the first and last addresses of the data to be altered are inputted to address registers 3 and 4. Next, the data to be substituted for the data of the ROM 1 are inputted through a data bus 10a to a P-ROM 6. When a mode signal is set at a high level, the address sent from a microprocessor unit MPU 7 is collated with the address inputted to the registers 3 and 4 by an address deciding circuit 2, and when it becomes the address in the range designated by the registers 3 and 4, the ROM 1 is altered to the ROM 6 by a switching circuit 8, and the address is read. Consequently, one part of the data of the mask ROM is altered. |
