| 摘要 |
PURPOSE:To attain required refresh even when a synchronizing signal is stopped by switching a signal source into a signal source changed properly in discriminat ing that a synchronizing signal applied externally is stopped and supplying the signal from the source as an internal synchronizing signal. CONSTITUTION:The leading of a signal fed to an external clock signal supply terminal 4 is detected by delay inverters 10, 11, 12 and a NAND gate 13 and the signal of active low level is generated. A self-exciting oscillation circuit 2 is not operated by said operation. Moreover, a signal fed to an external clock signal supply terminal 4 is outputted to an internal clock supply terminal 5 via a switching circuit 3. When a signal given to the external clock signal terminal 4 is unchanged, a ring oscillator composed of delay inverters 20, 21, capacitance components 23, 24 and an oscillation control NAND gate 22 starts its oscillation and the signal is given to an internal clock supply terminal 5 as an internal synchronizing clock through the switching circuit 3.
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