The basic task of any D/A converter is to take a binary number and convert it to an analog voltage or current. Traditional MCU D/A designs such as R-2R designs have problems that reduce the converter’s accuracy. They are sensitive to resistive loading and exhibit output drift with temperature. Also, their conversion time varies, depending on silicon speed and capacitive loading. Accurate on-chip D/As are rare because it is difficult to implement precision resistors on silicon using fabrication technology optimized for building microcontrollers. Moreover, because the analog Step size diminishes for each extra bit of resolution and MCU chips are inherently noisy, it is a challenge to increase the resolution above 8-bits. These problems and others are eliminated by a D/A design based on a counter whose output duty cycle can be varied under software control. Renesas’ solution is the all-digital 14-bit Pulse Width Modulation (PWM) design: the PWM14 D/A included on some H8 series MCUs. One benefit of the PWM approach is that it uses a low-impedance digital output circuit to drive a high impedance analog circuit. This virtually eliminates the effects of capacitive and resistive loading. Another benefit of the PWM14 design is that the resolution of the D/A is now a function only of the number of bits there are in the counter/compare circuit. Specifically, the resolution is 1/(2n-1), where n is the number of bits. Thus, Renesas’ 14-bit PWM D/A, which has 16,383 Steps, has a resolution of ±0.006%. Moreover, this resolution is totally unaffected by the problems that would otherwise be encountered if users had to implement precision analog D/A circuits in the digital process used to build the MCU.