MC68HC705P6A Datasheet, PDF (78/130 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Analog Subsystem
9.3 Analog Section
The following paragraphs describe the operation and performance of
analog modules within the analog subsystem.
9.3.1 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 will convert 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 referenced
to V_SS.
9.3.2 Reference 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.
9.3.3 Accuracy and Precision
The 8-bit conversion result is accurate to within ±1 1/2 LSB, including
quantization; however, the accuracy of conversions is tested and
guaranteed only with external oscillator operation.
9.4 Conversion Process
The A/D reference inputs are applied to a precision digital-to-analog
converter. Control logic drives the D/A and the analog output is
successively compared to the selected analog input which was sampled
at the beginning of the conversion cycle. The conversion process is
monotonic and has no missing codes.
Advance Information
78
Analog Subsystem
MC68HC705P6A — Rev. 2.0
MOTOROLA