HT46C62 datasheet(21/46 Pages) HOLTEK

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HT46R62/HT46C62

Rev. 1.60

July 14, 2005

A/D Converter

The 6 channels and 9 bits resolution A/D converter are

implemented in this microcontroller. The reference volt-

age is VDD. The A/D converter contains 4 special regis-

ters which are; ADRL (24H), ADRH (25H), ADCR (26H)

and ACSR (27H). The ADRH and ADRL are A/D result

read-only. After the A/D conversion is completed, the

ADRH and ADRL should be read to get the conversion

result data. The ADCR is an A/D converter control regis-

ter, which defines the A/D channel number, analog

channel select, start A/D conversion control bit and the

end of A/D conversion flag. If the users want to start an

A/D conversion, define PB configuration, select the con-

verted analog channel, and give START bit a rising edge

and falling edge (0

®1®0). At the end of A/D conver-

sion, the EOCB bit is cleared. The ACSR is A/D clock

setting register, which is used to select the A/D clock

source.

The A/D converter control register is used to control the

A/D converter. The bit2~bit0 of the ADCR are used to

select an analog input channel. There are a total of six

channels to select. The bit5~bit3 of the ADCR are used

to set PB configurations. PB can be an analog input or

as digital I/O line decided by these 3 bits. Once a PB line

is selected as an analog input, the I/O functions and

pull-high resistor of this I/O line are disabled and the A/D

converter circuit is powered-on. The EOCB bit (bit6 of

the ADCR) is end of A/D conversion flag. Check this bit

to know when A/D conversion is completed. The START

bit of the ADCR is used to begin the conversion of the

A/D converter. Giving START bit a rising edge and fall-

ing edge means that the A/D conversion has started. In

order to ensure that the A/D conversion is completed,

the START should remain at

²0² until the EOCB is

cleared to

²0² (end of A/D conversion).

Bit 7 of the ACSR register is used for test purposes only

and must not be used for other purposes by the applica-

tion program. Bit1 and bit0 of the ACSR register are

used to select the A/D clock source.

When the A/D conversion has completed, the A/D inter-

rupt request flag will be set. The EOCB bit is set to

²1²

when the START bit is set from

²0² to ²1².

Important Note for A/D initialization:

Special care must be taken to initialize the A/D con-

verter each time the Port B A/D channel selection bits

are modified, otherwise the EOCB flag may be in an un-

defined condition. An A/D initialization is implemented

by setting the START bit high and then clearing it to zero

within 10 instruction cycles of the Port B channel selec-

tion bits being modified. Note that if the Port B channel

selection bits are all cleared to zero then an A/D initial-

ization is not required.

Bit No.

Label

Function

ADCS0

ADCS1

Selects the A/D converter clock source

00= system clock/2

01= system clock/8

10= system clock/32

11= undefined

2~6

Unused bit, read as

²0²

TEST

For test mode used only

ACSR (27H) Register

Bit No.

Label

Function

ACS0

ACS1

ACS2

Defines the analog channel select.

PCR0

PCR1

PCR2

Defines the port B configuration select. If PCR0, PCR1 and PCR2 are all zero, the ADC circuit is

power off to reduce power consumption

EOCB

Indicates end of A/D conversion. (0 = end of A/D conversion)

Each time bits 3~5 change state the A/D should be initialized by issuing a START signal, other-

wise the EOCB flag may have an undefined condition. See

²Important note for A/D initialization².

START Starts the A/D conversion. (0

®1®0= start; 0®1= Reset A/D converter and set EOCB to ²1²)

ADCR (26H) Register

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