Patent ID: 7721083

Claim:
A CPU runaway determination circuit in a system, comprising: a CPU for executing a task; and a watchdog timer which has a counter that starts counting upon reception of a start signal from the CPU, and outputs a reset signal when the counter reaches a preset count value, wherein the watchdog timer has a register in which a clear pattern corresponding to the task is set by the CPU, the clear pattern in the register is rewritten into an initial value by a reset signal from a power section, the CPU reads the clear pattern held in the register when the system is booted up so as to determine whether the boot-up is caused by a reset by the reset signal from the power section or a reset by the reset signal from the watchdog timer, and when it is determined that the boot-up is caused by the reset by the reset signal from the watchdog timer, the CPU boots up the system so as not to restart the task corresponding to the clear pattern held in the register.