| 摘要 |
PURPOSE:To prevent data from being destructed due to the fluctuation of a power source for a RAM by controlling a switching means short-circuiting a resistance which is serially connected between the power source for the RAM and an external terminal so as to turn ON when the RAM is accessed. CONSTITUTION:When a memory card 20 is inserted into a main body, the power source voltage of the RAM 21 starts rising to the power source voltage 5V of the main body from 3V of a battery 22. At that time the base terminal of a transistor 26 is connected to the main body through the external terminal 210, and goes to a level H due to a signal from the interior of the main body. Thus, the transistor 26 is turned OFF. Hence the power source voltage of the RAM 21 is smoothly boosted by the time constant of the resistance 23 and a capacitor 24. On the other hand, when the RAM is accessed, the base terminal of the transistor 26 goes to a level L due to the signal from the main body, which results in the turning ON of the transistor 26. Consequently the impedance of the power source can be sufficiently dropped, and the value of the resistance 23 can be set to a value from which a necessary time constance is available.
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