HT66F13 datasheet(116/173 Pages) HOLTEK

116 / 173 page

The accompanying diagram shows graphically the various stages involved in an analog to digital

conversion process and its associated timing. After an A/D conversion process has been initiated by

the application program, the microcontroller internal hardware will begin to carry out the conversion,

during which time the program can continue with other functions. The time taken for the A/D

conversion is 16 tADCK where tADCK is equal to the A/D clock period.

Programming Considerations

During microcontroller operates 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 devices contain 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 VDD or VREF voltage, this gives a single bit analog

input value of VDD or VREF divided by 4096.

1 LSB= (VDD or VREF)

¸ 4096

The A/D Converter input voltage value can be calculated using the following equation:

A/D input voltage = A/D output digital value

´ (VDD or VREF) ¸ 4096

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 VDD or VREF level.

HT66F13/HT66F14/HT66F15

Enhanced A/D Flash Type MCU

Rev. 1.10

116

February 9, 2011

t A D C

A / D c o n v e r s i o n t i m e

0 1 1 B

0 1 0 B

S T A R T

E O C B

A C S 4 ,

A C S 1 , A C S 0

P o w e r - o n

R e s e t

E n d o f A / D

c o n v e r s i o n

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

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

A / D s a m p l i n g t i m e

t A D S

0 0 0 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

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

A / D s a m p l i n g t i m e

t A D S

o f f

o n

t O N 2 S T

t A D C

A / D c o n v e r s i o n t i m e

o f f

A D O F F

A D C M o d u l e

O N

A/D Conversion Timing

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