HT46R46E datasheet(35/73 Pages) HOLTEK

35 / 73 page

HT46R46E/C46E/R47E/C47E/R48AE/C48AE/R49E

Rev. 1.20

August 15, 2007

The following timing diagram shows graphically the various stages involved in an analog to digital conversion process

and its associated timing.

The setting up and operation of the A/D converter func-

tion is fully under the control of the application program as

there are no configuration options associated with the

A/D converter. 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 de-

pendent upon the device chosen and is a function of the

A/D clock period tAD as shown in the table.

Device

A/D Conversion Time

HT46R46E

64tAD

Other Devices

76tAD

A/D Conversion Time

Programming Considerations

When programming, special attention must be given to

the A/D channel selection bits in the ADCR register. If

these bits are all cleared to zero no external pins will be

selected for use as A/D input pins allowing the pins to be

used as normal I/O pins. When this happens the power

supplied to the internal A/D circuitry will be reduced re-

sulting in a reduction of supply current. This ability to re-

duce power by turning off the internal A/D function by

clearing the A/D channel selection bits may be an impor-

tant consideration in battery powered applications.

Another important programming consideration is that

when the A/D channel selection bits change value the

A/D converter must be re-initialised. This is achieved by

pulsing the START bit in the ADCR register immediately

after the channel selection bits have changed state. The

exception to this is where the channel selection bits are

all cleared, in which case the A/D converter is not re-

quired to be re-initialised.

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.

0 0 0 B

0 1 1 B

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 B 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

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 0 B

1 . P B p o r t s e t u p a s I / O s

2 . A / D c o n v e r t e r i s p o w e r e d o f f

t o r e d u c e p o w e r c o n s u m p t i o n

1 0 0 B

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

D o n ' t c a r e

E n d o f A / D

c o n v e r s i o n

E n d o f A / D

c o n v e r s i o n

S T A R T b i t s e t h i g h w i t h i n o n e t o t e n i n s t r u c t i o n c y c l e s a f t e r t h e P C R 0 ~ P C R 2 b i t s c h a n g e s t a t e

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

N o t e :

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

3 2 t A D

t A D C

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

t A D C

A/D Conversion Timing

Example: using an EOCB polling method to detect the end of conversion for the HT46R46E

clr

EADI

; disable ADC interrupt

mov

a,00000001B

mov

ACSR,a

; setup the ACSR register to select fSYS/8 as

; the A/D clock

mov

a,00100000B

; setup ADCR register to configure Port PB0~PB3

; as A/D inputs

mov

ADCR,a

; and select AN0 to be connected to the A/D

; converter

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