The SLA7042M and SLA7044M are designed for high-efficiency and high-performance microstepping operation of 2-phase, unipolar stepper motors. Microstepping provides improved resolution without limiting step rates, and provides much smoother low-speed motor operation. An automated, innovative packaging technology combined with power NMOS FETs and monolithic CMOS logic/control circuitry advances power multi-chip modules (PMCMsTM) toward the complete integration of motion control. Each half of these stepper motor controller/drivers operate independently. The 4-bit shift registers are serially loaded with motor phase information and output current-ratio data (eight levels). The combination of user-selectable current-sensing resistor, linearly adjustable reference voltage, and digitally selected output current ratio provides users with a broad, variable range of of full, half, and microstepping motor control (IOUT [VREF/3 RS] Current Ratio).