Electronic Design

Turn an 8-pin microcontroller into a programmable fractional divider

The PIC12C508 is an 8-pin microcontroller that contains an RC oscillator (4 MHz) and power-on-reset circuitry. Two pins are for ground and power-supply connections, while the remaining six pins are dedicated for input/output. This tiny microcontroller provides a low-cost and spacesaving solution for some applications that require fewer parts than if conventional logic devices are used.

The circuit shown is used to implement a fractional divider using the PIC12C508 (see the figure). The divide ratio produced is completely controlled by software. The microcontroller can divide an input signal by a factor of 1.5 to 16.5. D0-D3 selects the divide ratio. Note that the speed of the circuit is limited by the microcontroller’s execution time. It can work reliably under 30 kHz with a minimum input pulse width of 6 µs.

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