| 摘要 |
<p>PURPOSE:To deal with the increase request for SFR and RAM without increasing the capacity of memory device by arranging the SFR on the same memory space at the RAM and selectively using the memory space by switching modes. CONSTITUTION:A mode flag register 12 is connected to a control register (SFR) in a memory device 1 at the level 'L' state in the initial state and the data controlling a peripheral device 11 is set from the CPU 10 to the SFR. After setting such data to the SFR, the CPU 10 outputs a signal according to a mode setting instruction included in a program through a mode flag control line 5. The mode flag register 12 is made an 'H' level state and a databus 3 is connected to the RAM. As the result, the memory space from an address 00 used as the SFR to an address FF under the mode using the SFR can be used as the RAM under the mode using the RAM by switching the mode to be used. Thus, the RAM area can be expanded.</p> |
