Analog-to-Digital Converter (ADC)
Notes:
The MC68HC705P6A incorporates a 4-channel version of the 8-bit analog-to-digital converter (ADC) used on several 68HC05 devices.
The ADC is a ratiometric, fully monotonic, successive approximation converter. It has an analog multiplexer that supports up to eight input channels and also allows the high and low references and one half the difference between references to be read for calibration purposes.
Pins used by the ADC may also be used as inputs and sometimes outputs. Total converter accuracy is ±1 or ±1.5 LSB when its channels are input-only or bi-directional pins, respectively. The converter’s high reference voltage is supplied by a separate pin. The low reference input, when not bonded to an external pin, is internally tied to VSS.
Each single channel conversion requires 32 internal clock cycles. A separate RC oscillator, enabled under software control, can clock the ADC when MCU operating frequencies are below 1 MHz.
The converter is disabled on power-up and is enabled by setting the ADON bit in the A/D status and control register. Once enabled, conversions continue until the ADON bit is cleared or the MCU enters low-power stop mode.