State machine in which subsequent state can be directly inputted externally and transition can be stopped retaining the current state

摘要

A state machine that can be tested easily is disclosed. A state machine has a latch for storing data representing an intended state and a state control unit for producing data representing a subsequent state according to an intended state provided by the latch and a detection signal, and makes state transitions consecutively. The state machine comprises a state data input unit for inputting data representing an intended state directly from an external unit, a selector for selecting either data provided by the state control unit or data provided by the state data input unit so as to supply selected data as data representing a subsequent state to the latch, and a control data input unit for externally inputting control data for use in controlling the selection performed by the selector. After data representing an intended state is fed to the state data input unit, when control data requesting the selector to select data provided by the state data input unit and to send the data to the latch is input via the control data input unit, the latch latches data representing an intended state synchronously with a clock and thus retains the intended state.