DS18S20 查看數據表（PDF） - Maxim Integrated

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DS18S20

High-Precision 1-Wire Digital Thermometer

Maxim Integrated 

Figure 1. DS18S20 Block Diagram

VPU

4.7k

DQ

GND

PARASITE POWER

CIRCUIT

INTERNAL VDD

CPP

64-BIT ROM

AND

1-Wire PORT

VDD

POWER-

SUPPLY

SENSE

DS18S20

MEMORY CONTROL

LOGIC

DS18S20

SCRATCHPAD

TEMPERATURE SENSOR

ALARM HIGH TRIGGER (TH)

REGISTER (EEPROM)

ALARM LOW TRIGGER (TL)

REGISTER (EEPROM)

8-BIT CRC GENERATOR

OPERATION—MEASURING TEMPERATURE

The core functionality of the DS18S20 is its direct-to-digital temperature sensor. The temperature sensor

output has 9-bit resolution, which corresponds to 0.5°C steps. The DS18S20 powers-up in a low-power

idle state; to initiate a temperature measurement and A-to-D conversion, the master must issue a Convert

T [44h] command. Following the conversion, the resulting thermal data is stored in the 2-byte

temperature register in the scratchpad memory and the DS18S20 returns to its idle state. If the DS18S20

is powered by an external supply, the master can issue “read-time slots” (see the 1-Wire Bus System

section) after the Convert T command and the DS18S20 will respond by transmitting 0 while the

temperature conversion is in progress and 1 when the conversion is done. If the DS18S20 is powered with

parasite power, this notification technique cannot be used since the bus must be pulled high by a strong

pullup during the entire temperature conversion. The bus requirements for parasite power are explained in

detail in the Powering the DS18S20 section.

The DS18S20 output data is calibrated in degrees centigrade; for Fahrenheit applications, a lookup table

or conversion routine must be used. The temperature data is stored as a 16-bit sign-extended two’s

complement number in the temperature register (see Figure 2). The sign bits (S) indicate if the

temperature is positive or negative: for positive numbers S = 0 and for negative numbers S = 1. Table 1

gives examples of digital output data and the corresponding temperature reading.

Resolutions greater than 9 bits can be calculated using the data from the temperature, COUNT REMAIN

and COUNT PER °C registers in the scratchpad. Note that the COUNT PER °C register is hard-wired to

16 (10h). After reading the scratchpad, the TEMP_READ value is obtained by truncating the 0.5°C bit

(bit 0) from the temperature data (see Figure 2). The extended resolution temperature can then be

calculated using the following equation:

TEMPERATURE = TEMP _ READ − 0.25 + COUNT _ PER _ C − COUNT _ REMAIN

COUNT _ PER _ C

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