Electronic Design

8-Bit MCUs Harness Motor Control

Symbiotic peripherals make motor control manageable. Many 8-bit microcontrollers have been used for motor control. But performance always limits these chips to relatively simple applications, while systems that are more complex turn to DSPs.

Microchip includes peripherals such as a 14-bit, center-aligned pulse-width-modulation (PWM) device on-chip in its PIC18Fxx31 family. The PWM supports the usual edge-aligned synchronization, but center-aligned has better motor performance as well.

The PIC18Fxx31 incorporates a quadrature encoder and a high-speed analog-to-digital converter (ADC). The five- or nine-channel ADC actually has two channels that can be synchronized with each other and the PWM. This significantly improves system accuracy by capturing information at key points in the control process. In particular, the pair of converters will typically record the motor current and voltage.

The PIC18Fxx31 chips include an on-chip oscillator that is part of a fail-safe clock monitor system that tracks the external clock. The internal clock automatically kicks in if the external clock fails.

The MCUs integrate 8 or 16 kbytes of flash memory, 768 bytes of RAM, and 256 bytes of EEPROM. The systems include six- or eight-channel PWMs, a serial port, and four timers.

Pricing for the PIC18Fxx31 starts at $4.61. The chips come in a variety of packages.


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