| 摘要 |
PURPOSE:To extend an address irrespective of a function of a microprocessor by providing a pair of latching circuits and a selector circuit, setting an extension use address bit, and selecting one of latched addresses. CONSTITUTION:At the time of initialization, first of all, OH is set by a latching circuit 2, and 1M byte consisting of addresses 000000H-0FFFFFH is used as a program area. Subsequently, in the case of reading a program by a microprocessor, an output of the circuit 2 is selected through a signal line 4 and a data value becomes 0H on a signal line 8. Therefore, the program area of 000000H-0FFFFFH is brought to an access, and the program is read. Also, in the case of executing an access to a data area of 100000H-FFFFFFH, the upper 4 bits of an address of a data area to be brought to an access are set to a latching circuit 1, and thereafter, an address of the lower 20 bits of 000000H-FFFFFFH is set from the side of the microprocessor. In such a way, a memory area can be extended arbitrarily.
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