PURPOSE: To perform scan-in/out operations without changing contents of a latch by setting an FF to the data holding mode and setting clocks to 0 to perform scan-in/out operations after clocks are stopped.

CONSTITUTION: If a trouble occurs in the clock stop mode, a clock CCLO is stopped in the state of "0" or "1". If the clock CCLO is stopped in the state of "0", this stop is independent of operations; but if the clock CCLO is stopped in the state of "1", a JKFF6 is set to the data holding mode when a signal SCBSY =0 for start of scan-in/out is issued. Thereafter, when a clock blocking signal CINH=0 is issued, the CLK terminal of the JKFF6 is changed to "0" from "0" or "1". Though change of the CLK terminal from "1" to "0" indicates that the clock CCLO is inputted to the CLK terminal, contents are not changed because the JKFF6 is set to the data holding mode. Then, a clock SCAN CLOCK is issued to perform scan-in/out operations.