HT48R005 datasheet(40/62 Pages) HOLTEK

40 / 62 page

HT48R005/HT46R005

Rev. 1.00

November 29, 2011

fSYS

A/D Clock Period (tADCK)

ADCS2,

ADCS1,

ADCS0=000

(fSYS/2)

ADCS2,

ADCS1,

ADCS0=001

(fSYS/8)

ADCS2,

ADCS1,

ADCS0=010

(fSYS/32)

ADCS2,

ADCS1,

ADCS0=100

(fSYS)

ADCS2,

ADCS1,

ADCS0=101

(fSYS/4)

ADCS2,

ADCS1,

ADCS0=110

(fSYS/16)

ADCS2,

ADCS1,

ADCS0=011,

111

1MHz

ms8ms32ms1ms4ms16ms

Undefined

2MHz

ms4ms16ms

500ns

ms8ms

Undefined

4MHz

500ns

ms8ms

250ns*

ms4ms

Undefined

8MHz

250ns*

ms4ms

125ns*

500ns

Undefined

12MHz

167ns*

667ns

2.67

83ns*

333ns*

Undefined

A/D Clock Period Examples

A/D Input Pins

All of the A/D analog input pins are pin-shared with the

I/O pins on Port A as well as other functions. The PCR2~

PCR0 bits in the ADCR register, determine whether the

input pins are setup as A/D converter analog inputs or

whether they have other functions. If the PCR2~PCR0

bits for its corresponding pin is set high then the pin will

be setup to be an A/D converter input and the original

pin functions disabled. In this way, pins can be changed

under program control to change their function between

A/D inputs and other functions. All pull-high resistors,

which are setup through register programming, will be

automatically disconnected if the pins are setup as A/D

inputs. Note that it is not necessary to first setup the A/D

pin as an input in the PAC port control register to enable

the A/D input as when the PCR2~PCR0 bits enable an

A/D input, the status of the port control register will be

overridden.

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 ADCS2~ADCS0 in the ACSR regis-

ter.

· Step 2

Select which pins are to be used as A/D inputs and

configure them by correctly programming the

PCR2~PCR0 bits in the ADCR register.

· Step 3

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

ACSR register to zero.

· Step 4

Select which channel is to be connected to the internal

A/D converter by correctly programming the

ACS1~ACS0 bits which are also contained in the

ADCR register.

· Step 5

If the interrupts are to be used, the interrupt control

registers must be correctly configured to ensure the

A/D converter interrupt function is active. The master

interrupt control bit, EMI, and the A/D converter inter-

rupt bit, EADI, must both be set high to do this.

· Step 6

The analog to digital conversion process can now be

initialised by setting the START bit in the ADCR regis-

ter from low to high and then low again. Note that this

bit should have been originally cleared to zero.

· 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 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

When programming, special attention must be given to

the PCR[2:0] bits in the 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 internal A/D circuitry

will be power down. Setting the ADONB bit high has the

ability to power down the internal A/D circuitry, which

may be an important consideration in power sensitive

applications.

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