| 摘要 |
<p>PURPOSE:To reduce the power consumption not only at a CPU but other parts by attaining a constitution where a key input monitor circuit holds the CPU and at the same time reduces the power supply voltage if no key input occurs for a prescribed period. CONSTITUTION:A key input monitoring part 11 reads the data or the addresses emerging on a system bus 9 in the prescribed monitoring timing and collates them with a held specific instruction code or address. When the coincidence is secured in the collation, a counter is counted up. Then a signal of a high level is outputted to a signal line S2 connected to an interruption terminal INT of a CPU 1 via an OR gate 13 when the counter has an overflow. Thus the CPU 1 is set in a holding state and therefore the power consumption of the CPU 1 is reduced. At the same time, a power circuit 10 receives the signal of a high level from the line S2 and reduces the DC voltage supplied to a work RAM 3 or a VRAM 4 down to a level equal to the back-up voltage. In addition, the circuit 10 stops the supply of power to a liquid crystal display part 6 in order to discontinue the display working of the part 6.</p> |
