HT46R53 datasheet(18/42 Pages) HOLTEK

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HT46R53/HT46R54

Rev. 1.40

July 12, 2005

A/D Converter

The 8 channels 12-bit resolution A/D converter are im-

plemented in this microcontroller.

The A/D converter contains 4 special registers which

are; ADRL (20H), ADRH (21H), ADCR (22H) and ACSR

(23H). The ADRH and ADRL are A/D result register

higher-order byte and lower-order byte and are

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 raising

edge and falling edge (0

®1®0). At the end of A/D con-

version, the EOCB bit is cleared and an A/D converter

interrupt occurs (if the A/D converter interrupt is en-

abled). 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 are used to select an

analog input channel. There are a total of eight 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 determined by these 3 bits. Once a PB line is se-

lected as an analog input, the I/O functions and pull-high

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

verter circuit is powered on. The EOCB bit (bit6 of the

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

know when the A/D conversion is completed.

The START bit of the ADCR is used to begin the conver-

sion of the A/D converter. Giving START bit a rising edge

and falling 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 application

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 initialisation:

Special care must be taken to initialise 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 initialisation 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 initialis-

ation 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 (23H) Register

Bit No. Label

Function

ACS0

ACS1

ACS2

Defines the analog channel select

PCR0

PCR1

PCR2

Defines the port B configuration se-

lect. If PCR0, PCR1 and PCR2 are all

zero, the ADC circuit is powered 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 initialised by issuing a

START signal, otherwise the EOCB

flag may have an undefined condition.

See

²Important note for A/D initialis-

ation

².

START

Starts the A/D conversion.

®1®0= Start

®1= Reset A/D converter and set

EOCB to

²1².

ADCR (22H) Register

ACS2

ACS1

ACS0

Analog Channel

000

AN0

001

AN1

010

AN2

011

AN3

100

AN4

101

AN5

110

AN6

111

AN7

Analog Input Channel Selection

ADRL

(20H)

0000

ADRH

(21H)

D11 D10 D9

Note:

D0~D11 is A/D conversion result data bit

LSB~MSB.

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