| 摘要 |
PROBLEM TO BE SOLVED: To provide a clock signal self-test circuit capable of self-testing a clock signal generated by a first power supply voltage using a circuit element operated by a second power supply voltage and preventing occurrence of short circuit current regardless of the status of the power supply voltages.SOLUTION: A clock signal self-test circuit has such a configuration that a clock signal generation circuit 14 is connected to a microcomputer 16 via a clock signal transmission line 25 and a clock signal can be tested by a timer counter 19. A power supply circuit 8 generates a power supply voltage VA when a battery 4 is connected to a substrate 2, but a power supply circuit 9 does not generate a power supply voltage VB when a power supply switch 13 is off, and a load circuit 15 and the microcomputer 16 stop their operations. At this time, a switching circuit 27 electrically cuts off the connection between an output terminal 14a of the clock generation circuit 14 and an input terminal 16a of the microcomputer 16. As a result, a short circuit current is prevented from flowing from the clock signal generation circuit 14 to a power supply line 11 via the clock signal transmission line 25 and an input protection diode of the timer counter 19. |
