HT46R46 datasheet(27/77 Pages) HOLTEK

27 / 77 page

HT46R46/C46/R47/C47/R48A/C48A/R49

Rev. 1.30

June 5, 2008

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

Each of the devices contains a 4-channel analog to digi-

tal converter which can directly interface to external an-

alog signals, such as that from sensors or other control

signals and convert these signals directly into either an

8-bit or 9-bit digital value.

Device

Input

Channels

Conversion

Bits

Input Pins

HT46R46

PB0~PB3

HT46R47

PB0~PB3

HT46R48A

PB0~PB3

HT46R49

PB0~PB3

The following diagram shows the overall internal struc-

ture of the A/D converter, together with its associated

registers.

A/D Converter Data Registers - ADR, ADRL, ADRH

For the HT46R46 device, which has an 8-bit A/D con-

verter, a single register, known as ADR, is used to store

the 8-bit analog to digital conversion value. For the re-

maining devices, which have a 9-bit A/D converter, two

registers are required, 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. For devices which use two A/D

Converter Data Registers, note that only the high byte

byte register utilises only 1 bit of its 8-bit contents as it

contains only the lowest bit of the 9-bit converted value.

In the following tables, D0~D8 are the A/D conversion

data result bits.

Bit

ADR

A/D Data Register - HT46R46

Bit

ADRL

¾¾¾¾¾¾¾

ADRH

A/D Data Register - Other Devices

A/D Converter Control Register - ADCR

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

verter, a control register known as ADCR is provided.

This 8-bit register defines functions such as the selec-

tion of which analog channel is connected to the internal

A/D converter, which pins are used as analog inputs and

which are used as normal I/Os as well as controlling the

start function and monitoring the A/D converter end of

conversion status.

One section of this register contains the bits

ACS2~ACS0 which define the channel number. As each

of the devices contains only one actual analog to digital

converter circuit, each of the individual 4 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 inter-

nal A/D converter. Note that the ACS2 bit must always

be assigned a zero value.

A D C S o u r c e

f S Y S / 2

¸ N

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

A D C

V D D

P B 0 / A N 0

P B 1 / A N 1

P B 2 / A N 2

P B 3 / A N 3

A / D r e f e r e n c e v o l t a g e

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

P i n C o n f i g u r a t i o n

B i t s

C h a n n e l S e l e c t

B i t s

S t a r t B i t

C l o c k D i v i d e

R a t i o

E n d o f

C o n v e r s i o n B i t

A D R

o r

A D R L

A D R H

A / D D a t a

R e g i s t e r s

A/D Converter Structure

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