Holtek HT66F20-1 Manual page 138

A D O F F
o f f
A D C M o d u l e O N
S T A R T
E O C B
0 0 1 1 B
A C S 4 , A C S 2 ~ A C S 0
P o w e r - o n
R e s e t
R e s e t A / D
c o n v e r t e r
1 : D e f i n e p o r t c o n f i g u r a t i o n
2 : S e l e c t a n a l o g c h a n n e l
Programming Considerations
During microcontroller operations where the A/D converter is not being used, the A/D internal
circuitry can be switched off to reduce power consumption, by setting bit ADOFF high in the
ADCR0 register. When this happens, the internal A/D converter circuits will not consume power
irrespective of what analog voltage is applied to their input lines. If the A/D converter input lines are
used as normal I/Os, then care must be taken as if the input voltage is not at a valid logic level, then
this may lead to some increase in power consumption.
A/D Transfer Function
As the HT66F30-1 contains a 12-bit A/D converter, its full-scale converted digitised value is equal
to FFFH. Since the full-scale analog input value is equal to the V
single bit analog input value of V
The A/D Converter input voltage value can be calculated using the following equation:
The diagram shows the ideal transfer function between the analog input value and the digitised
output value for the A/D converter. Except for the digitised zero value, the subsequent digitised
values will change at a point 0.5 LSB below where they would change without the offset, and the
last full scale digitised value will change at a point 1.5 LSB below the V
Rev. 1.40
HT66F20-1/HT66F30-1/HT68F20-1/HT68F30-1
t
O N 2 S T
o n
A / D s a m p l i n g t i m e A / D s a m p l i n g t i m e
t t
A D S A D S
0 0 0 0 B
0 0 1 0 B
S t a r t o f A / D S t a r t o f A / D
c o n v e r s i o n c o n v e r s i o n
R e s e t A / D
c o n v e r t e r
E n d o f A / D
c o n v e r s i o n
t
A D C
A / D c o n v e r s i o n t i m e A / D c o n v e r s i o n t i m e
A/D Conversion Timing
or V divided by 4096.
DD REF
1 LSB=(V
DD
A/D input voltage=A/D output digital value × (V
1�8
Flash MCU with EEPROM
0 0 0 1 B
S t a r t o f A / D
c o n v e r s i o n
R e s e t A / D
c o n v e r t e r
E n d o f A / D
c o n v e r s i o n
t
A D C
or V voltage, this gives a
DD REF
or V )÷4096
REF
or V )÷4096
DD REF
or V
DD REF
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o f f
o n
level.