HT66F20 datasheet(139/250 Pages) HOLTEK

139 / 250 page

HT66F20/HT66F30/HT66F40/HT66F50/HT66F60

HT66FU30/HT66FU40/HT66FU50/HT66FU60

Rev. 1.20

139

June 4, 2010

The accompanying diagram shows graphically the vari-

ous stages involved in an analog to digital conversion

process and its associated timing. After an A/D conver-

sion process has been initiated by the application pro-

gram, 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 16tADCK where tADCK is equal to the A/D

clock period.

Programming Considerations

During microcontroller operations where the A/D con-

verter 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 off-

set, and the last full scale digitised value will change at a

point 1.5 LSB below the VDD or VREF level.

A/D Programming Example

The following two programming examples illustrate how

to setup and implement an A/D conversion. In the first

example, the method of polling the EOCB bit in the

ADCR0 register is used to detect when the conversion

cycle is complete, whereas in the second example, the

A/D interrupt is used to determine when the conversion

is complete.

F F E H

(

)

A / D C o n v e r s i o n

R e s u l t

F F F H

F F D H

0 3 H

0 2 H

0 1 H

0 . 5 L S B

4 0 9 3 4 0 9 4 4 0 9 5 4 0 9 6

A n a l o g I n p u t V o l t a g e

1 . 5 L S B

V D D o r V R E F

4 0 9 6

Ideal A/D Transfer Function

HT66F20 Datasheet(PDF) 139 Page - Holtek Semiconductor Inc

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