Abstract: There is provided an oscillation circuit including: a main oscillation circuit that outputs a specific main clock to an internal circuit; a sub oscillation circuit that outputs a sub clock having a different frequency to the frequency of the main oscillation circuit; a first abnormality detection section that detects an abnormality according to a number of main clock cycles output from the main oscillation circuit within a predetermined period corresponding to sub clock outputs from the sub oscillation circuit; and a second abnormality detection section that detects an abnormality according to a frequency divided clock of the main clock output from the main oscillation circuit that has been frequency-divided and the sub clock output from the sub oscillation circuit.

Abstract: An oscillator circuit, having an inverter with input and output terminals interconnected through a feedback resistance, operates in two modes. In a first mode, the input and output terminals are coupled to an external crystal resonator. In a second mode, an external clock signal is supplied to the input terminal. In the second mode, the input terminal is disconnected from the output terminal, and in addition, the output-drive capacity of the inverter is reduced, or the output terminal of the inverter is held at a fixed potential.