Datasheet

Analog-to-Digital Converter (ADC)
Technical Data MC68HC908GR8 — Rev 4.0
82 Analog-to-Digital Converter (ADC) MOTOROLA
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. All other input voltages will result in $FF,
if greater than V
REFH
.
NOTE: Inside the ADC module, the reference voltage, V
REFH
is connected to the
ADC analog power V
DDAD
; and V
REFL
is connected to the ADC analog
ground V
DDAD
. Therefore, the ADC input voltage should not exceed the
analog supply voltages
For operation, V
DDAD
should be tied to the same potential as V
DD
via
separate traces
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.
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/IDMAS 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.
16 to17 ADC cycles
ADC frequency
Conversion time =
Number of bus cycles = conversion time x bus frequency
Frees
cale Semiconductor,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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