Freescale Semiconductor, Inc.
GENERAL RELEASE SPECIFICATION
9.2.3 Accuracy and Precision
8
2
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.
3
9.2.4 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.
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9.3 Digital Section
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The following paragraphs describe the operation and performance of digital
modules within the analog subsystem.
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9.3.1 Conversion Times
9
Each input conversion requires 32 PH2 clock cycles, which must be at a frequency
equal to or greater than 1 MHz.
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A
9.3.2 Internal versus External Oscillator
If the MCU PH2 clock frequency is less than 1 MHz (2 MHz external oscillator), the
internal RC oscillator (approximately 1.5 MHz) must be used for the A/D converter
clock. The internal RC clock is selected by setting the EERC bit in the EEPROG
register.
NOTE
The RC oscillator is shared with the EEPROM module. The RC
oscillator is disabled while the MCU is in stop mode.
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ANALOG-TO-DIGITAL CONVERTER
MC68HC805P18
9-2
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