HT46R92 datasheet(29/61 Pages) HOLTEK

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HT46R92

Rev. 1.10

November 5, 2008

Summary of A/D Conversion Steps

The following summarises the individual steps that

should be executed in order to implement an A/D con-

version process.

· Step 1

Select the required A/D conversion clock by correctly

programming bits ADCS1 and ADCS0 in the ACSR

· Step 2

Enable the A/D by clearing the ADONB bit in the

ACSR register.

· Step 3

Select which channel is to be connected to the internal

A/D converter by correctly programming the

ACS2~ACS0 bits which are also contained in the

ADCR register.

· Step 4

Select which pins on Port B are to be used as A/D in-

puts and configure them as A/D input pins by correctly

programming the PCR0~PCR2 bits in the ADCR reg-

ister. Note that this step can be combined with Step 2

into a single ADCR register programming operation.

· Step 5

If the interrupts are to be used, the interrupt control reg-

isters must be correctly configured to ensure the A/D

converter interrupt function is active. The master inter-

rupt control bit, EMI, in the INTC interrupt control regis-

ter must be set to

²1² and the A/D converter interrupt

bit, EADI, in the INTC register must also be set to

²1².

· Step 6

The analog to digital conversion process can now be

initialised by setting the START bit in the ADCR regis-

ter from

²0² to ²1² and then to ²0² again. Note that this

bit should have been originally set to

²0².

· Step 7

To check when the analog to digital conversion pro-

cess is complete, the EOCB bit in the ADCR register

can be polled. The conversion process is complete

when this bit goes low. When this occurs the A/D data

registers ADRL and ADRH can be read to obtain the

conversion value. As an alternative method, if the in-

terrupts are enabled and the stack is not full, the pro-

gram can wait for an A/D interrupt to occur.

Note:

When checking for the end of the conversion

process, if the method of polling the EOCB bit in

the ADCR register is used, the interrupt enable

step above can be omitted.

The accompanying timing diagram shows graphically

the various stages involved in an analog to digital con-

version 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 16tAD

where tAD is equal to the A/D clock period.

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 turned off 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. The

A/D can also be turned off by using the ADONB bit int he

ACSR register.

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 c o n v e r s i o n t i m e

0 0 0 B

x x x B

1 0 0 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 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 = t A D C S + n * t A D ; n = b i t c o u n t o f A D C r e s o l u t i o n

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

1 0 1 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

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

0 0 0 B

x x x B

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

A/D Conversion Timing

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