MC68HC705P9 Datasheet, PDF (132/160 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Analog-to-Digital Converter (ADC)
11.4.1.2 PC6/AN0–PC3/AN3
The multiplexer can select one of four external analog input channels
(AN0, AN1, AN2, or AN3) for sampling. The conversion takes 32 cycles.
The first 12 cycles sample the voltage on the selected input pin by
charging an internal capacitor. In the last 20 cycles, a comparator
successively compares the output of an internal D/A converter to the
sampled analog input. Control logic changes the D/A converter input one
bit at a time, starting with the MSB, until the D/A converter output
matches the sampled analog input. The conversion is monotonic and
has no missing codes. At the end of the conversion, the conversion
complete flag (CCF) becomes set, and the CPU takes two cycles to
move the result to the ADC data register.
NOTE: To prevent excess power dissipation, do not simultaneously use an I/O
port pin as a digital input and an analog input.
While the ADC is on, the selected analog input reads as logic zero. The
port C pins that are not selected read normally.
An analog input voltage equal to V_RH converts to digital $FF; an input
voltage greater than V_RH converts to $FF with no overflow. An analog
input voltage equal to V_SS converts to digital $00. For ratiometric
conversion, the source of each analog input should use V_RH as the
supply voltage and be referenced to V_SS.
The clock frequency must be equal to or greater than 1 þMHz. If the
internal clock frequency is less than 1þMHz, the internal RC oscillator
(nominally 1.5 MHz) must be used for the ADC conversion clock. Make
this selection by setting the ADRC bit to logic one in the ADC status and
control register.
11.5 Interrupts
The ADC cannot generate interrupt requests.
Technical Data
132
Analog-to-Digital Converter (ADC)
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MC68HC705P9 — Rev. 4.0
MOTOROLA