SEMICONDUCTOR INTEGRATED CIRCUIT AND CLOCK CONTROL METHOD

摘要

To suppress power consumption. External clocks (11) generated by an external oscillation circuit are monitored by an external clock monitoring part (14) that operates in accordance with low-rate RC clocks generated by a low-rate RC oscillation circuit (13). When the external clock monitoring part (14) determines an inputting of the external clocks (11), a control circuit (16) instructs an operation clock selecting part (15) to select the external clocks (11). Thus, the external clocks (11) are used as operation clocks. When the external clock monitoring part (14) determines that the inputting of the external clocks (11) has halted, an RCoscillation circuit (12) starts its operation, and the control circuit (16) instructs the operation clock selecting part (15) to select the outputs of the RC oscillation circuit (12). Thus, the RC clocks generated by the RC oscillation circuit (12) are selectively used as operation clocks.