| 摘要 |
PURPOSE:To expand a memory space and to assign the same memory to both a ROM and a RAM by adding the output of an F/F to an address signal outputted from a processor part and increasing the number of bits of the address signal substantially by one bit. CONSTITUTION:As to write, for example, when the write is executed to the first block and the second block of an RAM 3 and is completed, a CPU 1 outputs a set signal on a set signal line 11 and sets an F/F 9. The signal of output terminal Q of the F/F 9 is set to logic '1' and a ROM 2 is not selected regardless of the bit pattern of the high order three bits a10, a9 and a8 of the address signal in the condition that said signal is inputted in a ROM decoder 4 and a RAM decoder 5, but selected eight blocks of the RAM 3 corresponding to eight kinds of the bit pattern of the high order three bits a10, a9 and a8. This system is operated as a computer where all the memory spaces lie in the RAM. Therefore the write is executed to the area of program memory and the program can be changed.
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