The PD75518(A) is a 75X series four-bit single-chip microcomputer which enables data processing equivalent to that performed by an eight-bit microcomputer. It is a high-performance product, whose minimum instruction execution time is 0.67 s, shorter than 0.95 s for the conventional PD75516. The ROM and RAM capacities are also larger, and the throughput of the 75X series is further increased. The PD75517(A) is suited to controllers of electric parts of automobiles.