HT46R01M datasheet(44/69 Pages) HOLTEK

44 / 69 page

HT46R01M/HT46R02M/HT48R01M/HT48R02M

Rev. 1.10

March 8, 2010

fSYS

A/D Clock Period (tAD)

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

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. Bits PCR3~PCR0 in the register, de-

termine whether the input pins are setup as normal Port

A input/output pins or whether they are setup as analog

inputs. In this way, pins can be changed under program

control to change their function from normal I/O opera-

tion to analog inputs and vice versa. Pull-high resistors,

which are setup through register programming, apply to

the input pins only when they are used as normal I/O

pins, if setup as A/D inputs the pull-high resistors will be

automatically disconnected. Note that it is not neces-

sary 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

PCR3~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, ADCS1 and ADCS0 in the

· Step 2

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

· Step 3

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 reg-

ister.

· Step 4

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

configure them as A/D input pins by correctly pro-

gramming the PCR3~PCR0 bits in the ADCR register.

Note that this step can be combined with Step 3 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 INTC0 interrupt control reg-

ister must be set to

²1², register and the A/D converter

interrupt bit, ADE, in the INTC1 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 diagram shows graphically the vari-

ous 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 16tAD

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

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