MC68HC908GT16 Datasheet, PDF (92/412 Pages) Motorola, Inc – Microcontrollers

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:
The ADC input voltage must always be greater than V_SSA and less than
V_DDA. V_REFH must always be greater than or equal to V_REFL.
Connect the V_DDA pin to the same voltage potential as the V_DD pin, and
connect the V_SSA pin to the same voltage potential as the V_SS pin.
The V_DDA pin should be routed carefully for maximum noise immunity.
5.4.3 Conversion Time
Conversion starts after a write to the ADC status and control register
(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
92
MC68HC908GT16 • MC68HC908GT8 — Rev. 2
Analog-to-Digital Converter (ADC)
MOTOROLA