| 摘要 |
<p>PURPOSE:To decrease the number of pins of a CPU by sharing the input/output terminal of the CPU with a key input device to the CPU and a storage device. CONSTITUTION:The address output to a storage device 3 and the key output to a key input device 2 share the same pin of a CPU1. Under such conditions, a chip enable signal CE which is supplied to the device 3 from the CPU1 is set at a low level in a selection mode of the device 3. Thus the device 3 is applicable. In this case, the key input is inhibited to the CPU1 from the device 2. In a key input mode, the signal CE supplied to the device 3 is set at a high level, and the device 3 is inapplicable. Then the key input is possible to the CPU1 from the device 2.</p> |
