HMS87C1808B Datasheet, PDF(60/99 Page) List of Unclassifed Manufacturers

English

English German Russian Spanish Italian Polish Chinese Japanese Korean French Portuguese	Language :

HMS87C1808B Datasheet, PDF (60/99 Pages) List of Unclassifed Manufacturers – 8-BIT SINGLE-CHIP MICROCONTROLLERS

◁

HMS87C1X04B/08B/16B

15. ANALOG TO DIGITAL CONVERTER

The analog-to-digital converter (A/D) allows conversion of an

analog input signal to a corresponding 8-bit digital value. The A/

D module has eight analog inputs, which are multiplexed into one

sample and hold. The output of the sample and hold is the input

into the converter, which generates the result via successive ap-

proximation.

The analog reference voltage is selected to VDD or AVref by set-

ting of the bit AVREFS in RBFUNC register. If external analog

reference AVref is selected, the bit ANSEL0 should not be set to

â1â, because this pin is used to an analog reference of A/D con-

verter.

The A/D module has two registers which are the control register

ADCM and A/D result register ADCR. The ADCM register,

shown in Figure 15-2 , controls the operation of the A/D convert-

er module. The port pins can be configure as analog inputs or dig-

ital I/O.

To use analog inputs, each port is assigned analog input port by

setting the bit ANSEL[7:0] in RAFUNC register. And selected

the corresponding channel to be converted by setting ADS[2:0].

The processing of conversion start when the start bit ADST is set

to â1â. After one cycle, it is cleared by hardware. The register

ADCR contains the results of the A/D conversion. When the con-

version is completed, the result is loaded into the ADCR, the A/

D conversion status bit ADSF is set to â1â, and the A/D interrupt

flag ADIF is set. The block diagram of the A/D module is shown

in Figure 15-1 . The A/D status bit, ADSF is set automatically

when A/D conversion is completed, cleared when A/D conver-

sion is in process. The conversion time takes maximum 10 uS (at

fxin=8 MHz).

ADS[2:0]

RA7/AN7

RA6/AN6

RA5/AN5

RA4/AN4

RA3/AN3

RA2/AN2

RA1/AN1

RB0/AN0/AVref

111

ANSEL7

110

ANSEL6

101

ANSEL5

100

ANSEL4

011

ANSEL3

010

ANSEL2

001

ANSEL1

000

ANSEL0 (RAFUNC.0)

Sample & Hold

S/H

Resistor

Ladder

Circuit

A/D Result Register

ADCR(8-bit)

ADDRESS : EBH

RESET VALUE : Undefined

Successive

Approximation

Circuit

ADIF

A/D Interrupt

VDD Pin

ADEN

AVREFS (RBFUNC.0)

Figure 15-1 A/D Converter Block Diagram

SEP. 2004 Ver 1.03

▷