DS1820S Просмотр технического описания (PDF) - Dallas Semiconductor -> Maxim Integrated

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производитель

DS1820S

1–Wire™ Digital Thermometer

Dallas Semiconductor -> Maxim Integrated 

DS1820

DETAILED PIN DESCRIPTION

PIN

16–PIN SSOP

PIN

PR35 SYMBOL

DESCRIPTION

9

1

GND Ground.

8

2

DQ

Data Input/Output pin. For 1–Wire operation: Open drain. (See

“Parasite Power” section.)

7

3

VDD Optional VDD pin. See “Parasite Power” section for details of

connection.

DS1820S (16–pin SSOP): All pins not specified in this table are not to be connected.

OVERVIEW

The block diagram of Figure 1 shows the major compo-

nents of the DS1820. The DS1820 has three main data

components: 1) 64–bit lasered ROM, 2) temperature

sensor, and 3) nonvolatile temperature alarm triggers

TH and TL. The device derives its power from the

1–Wire communication line by storing energy on an

internal capacitor during periods of time when the signal

line is high and continues to operate off this power

source during the low times of the 1–Wire line until it

returns high to replenish the parasite (capacitor) supply.

As an alternative, the DS1820 may also be powered

from an external 5 volts supply.

Communication to the DS1820 is via a 1–Wire port. With

the 1–Wire port, the memory and control functions will

not be available before the ROM function protocol has

been established. The master must first provide one of

five ROM function commands: 1) Read ROM, 2) Match

ROM, 3) Search ROM, 4) Skip ROM, or 5) Alarm

Search. These commands operate on the 64–bit

lasered ROM portion of each device and can single out

a specific device if many are present on the 1–Wire line

as well as indicate to the Bus Master how many and

what types of devices are present. After a ROM function

sequence has been successfully executed, the memory

and control functions are accessible and the master

may then provide any one of the six memory and control

function commands.

One control function command instructs the DS1820 to

perform a temperature measurement. The result of this

measurement will be placed in the DS1820’s scratch-

pad memory, and may be read by issuing a memory

function command which reads the contents of the

scratchpad memory. The temperature alarm triggers

TH and TL consist of one byte EEPROM each. If the

alarm search command is not applied to the DS1820,

these registers may be used as general purpose user

memory. Writing TH and TL is done using a memory

function command. Read access to these registers is

through the scratchpad. All data is read and written

least significant bit first.

DS1820 BLOCK DIAGRAM Figure 1

MEMORY AND

CONTROL LOGIC

DQ

64–BIT ROM

AND

1–WIRE PORT

TEMPERATURE SENSOR

INTERNAL VDD

SCRATCHPAD

HIGH TEMPERATURE

TRIGGER, TH

POWER

VDD

SUPPLY

SENSE

8–BIT CRC

GENERATOR

LOW TEMPERATURE

TRIGGER, TL

030598 2/27

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