Power-on detection circuit and microcontroller
There is provided a power-on detection circuit including: a flip-flop circuit storing an indefinite value at the time of power-on and outputting plural-bit data; and a comparator comparing the plural-bit data output from the flip-flop circuit and a plural-bit fixed value and outputting a power-on detect flag depending on a comparison result thereof.
1. A power-on detection circuit comprising:
a plural-bit flip-flop circuit storing an unknown value at the time of power-on and outputting plural-bit data; and
a comparator comparing the plural-bit data output from the plural-bit flip-flop circuit and a plural-bit fixed value and outputting a power-on detect flag depending on a comparison result thereof,
wherein the plural-bit flip-flop circuit inputs the same value data as the fixed value from a CPU to store when the power-on detect flag indicating that the data and the fixed value are inconsistent with each other is output from the comparator.
2. The power-on detection circuit according to claim 1 , wherein
as for the plural-bit fixed value, the number of bits of 1 and the number of bits of 0 are the same.
3. The power-on detection circuit according to claim 1 , wherein
at the time of power-on, the plural-bit flip-flop circuit outputs data based on the unknown value and the comparator outputs the power-on detect flag indicating that the data and the fixed value are inconsistent with each other.
4. A microcontroller comprising:
a power-on detection circuit; and
a CPU, and wherein
the power-on detection circuit comprises:
a plural-bit flip-flop circuit storing an unknown value at the time of power-on and outputting plural-bit data; and
a comparator comparing the plural-bit data output from the plural-bit flip-flop circuit and a plural-bit fixed value and outputting a power-on detect flag depending on a comparison result thereof, and
the CPU outputs the same value data as the fixed value to the plural-bit flip-flop circuit to store when the power-on detect flag indicating that the data and the fixed value are inconsistent with each other is input from the comparator.
5. The microcontroller according to claim 4 , wherein
as for the plural-bit fixed value, the number of bits of 1 and the number of bits of 0 are the same.
6. The microcontroller according to claim 4 , wherein
at the time of power-on, the plural-bit flip-flop circuit outputs data based on the unknown value and the comparator outputs the power-on detect flag indicating that the data and the fixed value are inconsistent with each other.
7. The microcontroller according to claim 4 , wherein
the CPU performs a reset process depending on the power-on detect flag when a reset signal is input.
8. The microcontroller according to claim 7 , wherein
at the time of reset, the CPU performs a process to turn security on when the power-on detect flag indicating that the data and the fixed value are inconsistent with each other is input, and the CPU performs a process to continue a security state before reset when the power-on detect flag indicating that the data and the fixed value are consistent with each other is input.