Abstract: An in-system programmable logic device is disclosed which may be configured or reconfigured while installed in a user's system. The disclosed device employs non-volatile memory cells such as floating gate transistors as the programmable elements, and hence the device retains a particular programmed logic configuration virtually indefinitely during a powered-down state. The device is operable in a normal state and in several utility states for reconfiguring the device. The device state is controlled by an internal state machine which executes several state equations whose variables are the logic levels driving two dedicated pins and the present device state. One device pin receives serial input data which loads a shift register latch. The contents of the latch are employed to select a particular row of the cells to be programmed and the logic level to which the selected cells are to be programmed.