Nonvolatile flip-flop enables leakage power reduction in logic circuits and quick return from standby mode. However, it has limited write endurance, and its power consumption for writing is larger than that of conventional D flip-flop (DFF). For this reason, it is important to reduce the number of write operations. The write operations can be reduced by stopping the clock signal to synchronous flip-flops because write operations are executed only when the clock is applied to the flip-flops. In such clock gating, a method using Exclusive OR (XOR) of the current value and the new value as the control signal is well known. The XOR based method is effective, but there are several cases where the write operations can be reduced even if the current value and the new value are different. The paper proposes a method to detect such unnecessary write operations based on state transition analysis, and proposes a write control method to save power consumption of nonvolatile flip-flops. In the method, redundant bits are detected to reduce the number of write operations. If the next state and the outputs do not depend on some current bit, the bit is redundant and not necessary to write. The method is based on Binary Decision Diagram (BDD) calculation. We construct write control circuits to stop the clock signal by converting BDDs representing a set of states where write operations are unnecessary. Proposed method can be combined with the XOR based method and reduce the total write operations. We apply combined method to some benchmark circuits and estimate the power consumption with Synopsys NanoSim. On average, 15.0% power consumption can be reduced compared with only the XOR based method.

A Field Programmable Sequencer and Memory (FPSM), which is a programmable unit exclusively optimized for peripherals on a micro controller unit, is proposed. The FPSM functions as not only the peripherals but also the standard built-in memory. The FPSM provides easier programmability with a smaller area overhead, especially when compared with the FPGA. The FPSM is implemented on the FPGA and the programmability and performance for basic peripherals such as the 8 bit counter and 8 bit accuracy Pulse Width Modulation are emulated on the FPGA. Furthermore, the FPSM core with a 4K bit SRAM is fabricated in 0.18µm 5 metal CMOS process technology. The FPSM is an half the area of FPGA, its power consumption is less than one-fifth.