HT46R005 datasheet(41/62 Pages) HOLTEK

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HT48R005/HT46R005

Rev. 1.00

November 29, 2011

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 voltage, this gives a single bit analog input value of

VDD divided by 4096.

1 LSB= (VDD)

¸ 4096

The A/D Converter input voltage value can be calcu-

lated using the following equation:

A/D input voltage =

A/D output digital value

´ (VDD) ¸ 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 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

ADCR 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.

t A D C

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

0 0 0 B

x x x B

x x x B - P C R [ 2 : 0 ] i s n o t e q u a l t o " 0 "

0 1 0 B

S T A R T

E O C B

P C R 2 ~

P C R 0

A C S 2 ~

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

A / D c l o c k m u s t b e f s y s , f S Y S / 2 , f S Y S / 4 , f S Y S / 8 , f S Y S / 1 6 o r f S Y S / 3 2

t A D C S = 4 t A D

t A D C = 1 6 t A D

N o t e :

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 C 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 C S

A D C m o d u l e

O N

A D O N B

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

A/D Conversion Timing

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

4 0 9 6

Ideal A/D Transfer Function

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