HT45R37 datasheet(33/100 Pages) HOLTEK

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HT45R37

Rev. 1.10

January 29, 2010

Analog to Digital Converter

The need to interface to real world analog signals is a

common requirement for many electronic systems.

However, to properly process these signals by a

microcontroller, they must first be converted into digital

signals by A/D converters. By integrating the A/D con-

version electronic circuitry into the microcontroller, the

need for external components is reduced significantly

with the corresponding follow-on benefits of lower costs

and reduced component space requirements.

A/D Overview

The device contains an 6-channel analog to digital con-

verter which can directly interface to external analog sig-

nals, such as that from sensors or other control signals

and convert these signals directly into either a 12-bit dig-

ital value.

Input

Channels

Conversion

Bits

Input

Pins

PB0~PB5

The accompanying block diagram shows the overall in-

ternal structure of the A/D converter, together with its as-

sociated registers.

A/D Converter Data Registers

- ADRL, ADRH

The device, which has an internal 12-bit A/D converter,

requires two data registers, a high byte register, known

as ADRH, and a low byte register, known as ADRL. After

the conversion process takes place, these registers can

be directly read by the microcontroller to obtain the digit-

ised conversion value. Only the high byte register,

ADRH, utilises its full 8-bit contents. The low byte regis-

ter utilises only 4 bit of its 8-bit contents as it contains

only the lowest bits of the 12-bit converted value.

In the following table, D0~D11 is the A/D conversion

data result bits.

Bit

ADRL

¾¾¾¾

ADRH

D11 D10 D9

A/D Data Registers

A/D Converter Control Registers

- ADCR, ACSR

To control the function and operation of the A/D con-

verter, two control registers known as ADCR and ACSR

are provided. These 8-bit registers define functions

such as the selection of which analog channel is con-

nected to the internal A/D converter, which pins are

used as analog inputs and which are used as normal

I/Os, the A/D clock source as well as controlling the start

function and monitoring the A/D converter end of con-

version status.

The ACS2~ACS0 bits in the ADCR register define the

channel number. As the device contains only one actual

analog to digital converter circuit, each of the individual

6 analog inputs must be routed to the converter. It is the

function of the ACS2~ACS0 bits in the ADCR register to

determine which analog channel is actually connected

to the internal A/D converter.

The ADCR control register also contains the

PCR2~PCR0 bits which determine which pins on Port B

are used as analog inputs for the A/D converter and

which pins are to be used as normal I/O pins. Note that if

the PCR2~PCR0 bits are all set to zero, then all the Port

B pins will be setup as normal I/Os and the internal A/D

converter circuitry will be powered off to reduce the power

consumption.

The START bit in the register is used to start and reset

the A/D converter. When the microcontroller sets this bit

from low to high and then low again, an analog to digital

C l o c k

D i v i d e r

A C S R R e g i s t e r

A D C

P B 0 / A N 0

P B 1 / A N 1

P B 5 / A N 5

A / D

R e f e r e n c e

V o l t a g e

A D R L

A D R H

A / D D a t a

R e g i s t e r s

P C R 0 ~ P C R 2

A D C S 0 ~ A D C S 2

S T A R T

E O C B

A D C R

R e g i s t e r

A V S S

A / D G r o u n d

A V D D

A / D P o s i t i v e P o w e r S u p p l y

A D O N B B i t

A / D E n a b l e

f S Y S

A/D Converter Structure

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