INTEGRATED-CIRCUIT INCORPORATED OSCILLATION CIRCUIT

摘要

PROBLEM TO BE SOLVED: To secure restoring operation after resetting by starting output of one clock one cycle of a clock which is shorter between 1st and 2nd clocks after the output of the other clock is stopped when the latter clock is switched to the former clock. SOLUTION: An internal oscillation circuit 31 has inverters in an integrated circuit 1 and capacitors connected to their outputs, they are connected in series, and the output is fed back to the input. An external oscillation circuit 40 has external terminals 2 and 3 and is able to oscillate on a solid oscillation mode and a CR oscillation mode. An clock switching circuit 41 selects one of the 1st clock from a ring oscillator 31 and the 2nd clock from the external oscillation circuit 40 and outputs it as its internal clock. Here, when one clock is switched to the other, the latter clock beings to be outputted one cycle of the shorter clock after the output of the former clock is stopped.