MC68HC05P18A Datasheet, PDF (92/130 Pages) Freescale Semiconductor, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Analog-to-Digital (A/D) Converter
11.3 Analog Section
The following paragraphs describe the operation and performance of
analog modules within the analog subsystem.
11.3.1 Ratiometric Conversion
The A/D converter is ratiometric, with pin V_REFH supplying the high
reference voltage. Applying an input voltage equal to V_REFH produces a
conversion result of $FF (full scale). Applying an input voltage equal to
V_SS produces a conversion result of $00. An input voltage greater than
V_REFH converts to $FF with no overflow indication. For ratiometric
conversions, V_REFH should be at the same potential as the supply
voltage being used by the analog signal being measured and be
referenced to V_SS.
11.3.2 Reference Supply Voltage (V_REFH)
The reference supply for the A/D converter shares pin PC7 with port C.
The low reference is tied to the V_SS pin internally. V_REFH can be any
voltage between V_SS and V_DD; however, the accuracy of conversions is
tested and guaranteed only for V_REFH = V_DD.
11.3.3 Accuracy and Precision
The 8-bit conversion result is accurate to within ± 1 1/2 LSB (least
significant bit), including quantization; however, the accuracy of
conversions is tested and guaranteed only with external oscillator
operation.
11.4 Conversion Process
The A/D reference inputs are applied to a precision digital-to-analog
(D/A) converter. Control logic drives the D/A and the analog output is
successively compared to the selected analog input that was sampled at
Technical Data
Analog-to-Digital (A/D) Converter
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MC68HC05P18A