MC68HC908GP32 Datasheet, PDF (92/410 Pages) Motorola, Inc – M68HC08 Family of 8-bit microcontroller units (MCUs)

Freescale Semiconductor, Inc.
Analog-to-Digital Converter (ADC)
5.4.2 Voltage Conversion
When the input voltage to the ADC equals V_REFH, the ADC converts the
signal to $FF (full scale). If the input voltage equals V_REFL, the ADC
converts it to $00. Input voltages between V_REFH and V_REFL are a
straight-line linear conversion.
NOTE:
Inside the ADC module, the reference voltages V_REFH is connected to
the ADC analog power, V_DDAD; and V_REFL is connected to the ADC
analog ground, V_SSAD. Therefore, the ADC input voltage should not
exceed these analog supply voltages.
Connect the V_DDAD pin to the same voltage potential as the V_DD pin, and
connect the V_SSAD pin to the same voltage potential as the V_SS pin.
The V_DDAD pin should be routed carefully for maximum noise immunity.
5.4.3 Conversion Time
Conversion starts after a write to the ADSCR. One conversion will take
between 16 and 17 ADC clock cycles. The ADIVx and ADICLK bits
should be set to provide a 1-MHz ADC clock frequency.
Conversion time = ^{16 to 17 ADC cycles}
ADC frequency
Number of bus cycles = conversion time × bus frequency
5.4.4 Conversion
In continuous conversion mode, the ADC data register will be filled with
new data after each conversion. Data from the previous conversion will
be overwritten whether that data has been read or not. Conversions will
continue until the ADCO bit is cleared. The COCO bit is set after the first
conversion and will stay set until the next write of the ADC status and
control register or the next read of the ADC data register.
In single conversion mode, conversion begins with a write to the
ADSCR. Only one conversion occurs between writes to the ADSCR.
Technical Data
90
MC68HC908GP32•MC68HC08GP32 — Rev. 6
Analog-to-Digital Converter (ADC)
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