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1 of 20 043001

FEATURES

• Unique 1-wire interface requires only one

port pin for communication

• Each device has a unique 64-bit serial code

stored in an on-board ROM

• Multi-drop capability simplifies distributed

temperature sensing applications

• Requires no external components

• Can be powered from data line. Power supply

range is 3.0V to 5.5V

• Measures temperatures from –55°C to

+125°C (–67°F to +257°F)

• ±0.5°C accuracy from –10°C to +85°C

• Thermometer resolution is user-selectable

from 9 to 12 bits

• Converts temperature to 12-bit digital word in

750 ms (max.)

• User-definable nonvolatile alarm settings

• Alarm search command identifies and

addresses devices whose temperature is

outside of programmed limits (temperature

alarm condition)

• Software compatible with the DS1822

• Applications include thermostatic controls,

industrial systems, consumer products,

thermometers, or any thermally sensitive

system

PIN ASSIGNMENT

PIN DESCRIPTION

GND - Ground

DQ - Data In/Out

- Power Supply Voltage

NC - No Connect

DESCRIPTION

The DS18B20 Digital Thermometer provides 9 to 12–bit centigrade temperature measurements and has

an alarm function with nonvolatile user-programmable upper and lower trigger points. The DS18B20

communicates over a 1-wire bus that by definition requires only one data line (and ground) for

communication with a central microprocessor. It has an operating temperature range of –55°C to +125°C

and is accurate to ±0.5°C over the range of –10°C to +85°C. In addition, the DS18B20 can derive power

directly from the data line (“parasite power”), eliminating the need for an external power supply.

Each DS18B20 has a unique 64-bit serial code, which allows multiple DS18B20s to function on the same

1–wire bus; thus, it is simple to use one microprocessor to control many DS18B20s distributed over a

large area. Applications that can benefit from this feature include HVAC environmental controls,

temperature monitoring systems inside buildings, equipment or machinery, and process monitoring and

control systems.

DS18B20

Programmable Resolution

1-Wire

Digital Thermomete

www.dalsemi.com

8-pin 150-mil SOIC

(DS18B20Z)

TO-92

(

DS18B20

)

(

BOTTOM VIEW

)

2 3

DALLAS

18B20

GND

2 3

GND

DALLAS

18B20

Summary of content (20 pages)

PAGE 1
DS18B20 Programmable Resolution 1-Wire® Digital Thermometer www.dalsemi.com • • • • • • • • • • • • Unique 1-wire interface requires only one port pin for communication Each device has a unique 64-bit serial code stored in an on-board ROM Multi-drop capability simplifies distributed temperature sensing applications Requires no external components Can be powered from data line. Power supply range is 3.0V to 5.5V Measures temperatures from –55°C to +125°C (–67°F to +257°F) ±0.
PAGE 2
DS18B20 DETAILED PIN DESCRIPTIONS Table 1 8-PIN SOIC* TO-92 SYMBOL DESCRIPTION 5 1 GND Ground. 4 2 DQ Data Input/Output pin. Open-drain 1-wire interface pin. Also provides power to the device when used in parasite power mode (see “Parasite Power” section.) 3 3 VDD Optional VDD pin. VDD must be grounded for operation in parasite power mode. *All pins not specified in this table are “No Connect” pins. OVERVIEW Figure 1 shows a block diagram of the DS18B20, and pin descriptions are given in Table 1.
PAGE 3
DS18B20 OPERATION – MEASURING TEMPERATURE The core functionality of the DS18B20 is its direct-to-digital temperature sensor. The resolution of the temperature sensor is user-configurable to 9, 10, 11, or 12 bits, corresponding to increments of 0.5°C, 0.25°C, 0.125°C, and 0.0625°C, respectively. The default resolution at power-up is 12 bit. The DS18B20 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.
PAGE 4
DS18B20 OPERATION – ALARM SIGNALING After the DS18B20 performs a temperature conversion, the temperature value is compared to the userdefined two’s complement alarm trigger values stored in the 1-byte TH and TL registers (see Figure 3). The sign bit (S) indicates if the value is positive or negative: for positive numbers S = 0 and for negative numbers S = 1. The TH and TL registers are nonvolatile (EEPROM) so they will retain data when the device is powered down.
PAGE 5
DS18B20 The use of parasite power is not recommended for temperatures above 100°C since the DS18B20 may not be able to sustain communications due to the higher leakage currents that can exist at these temperatures. For applications in which such temperatures are likely, it is strongly recommended that the DS18B20 be powered by an external power supply. In some situations the bus master may not know whether the DS18B20s on the bus are parasite powered or powered by external supplies.
PAGE 6
DS18B20 MEMORY The DS18B20’s memory is organized as shown in Figure 7. The memory consists of an SRAM scratchpad with nonvolatile EEPROM storage for the high and low alarm trigger registers (TH and TL) and configuration register. Note that if the DS18B20 alarm function is not used, the TH and TL registers can serve as general-purpose memory. All memory commands are described in detail in the DS18B20 FUNCTION COMMANDS section.
PAGE 7
DS18B20 CONFIGURATION REGISTER Byte 4 of the scratchpad memory contains the configuration register, which is organized as illustrated in Figure 8. The user can set the conversion resolution of the DS18B20 using the R0 and R1 bits in this register as shown in Table 3. The power-up default of these bits is R0 = 1 and R1 = 1 (12-bit resolution). Note that there is a direct tradeoff between resolution and conversion time.
PAGE 8
DS18B20 check is available in Application Note 27 entitled “Understanding and Using Cyclic Redundancy Checks with Dallas Semiconductor Touch Memory Products.” CRC GENERATOR Figure 9 INPUT XOR XOR XOR (MSB) (LSB) 1-WIRE BUS SYSTEM The 1-wire bus system uses a single bus master to control one or more slave devices. The DS18B20 is always a slave.
PAGE 9
DS18B20 TRANSACTION SEQUENCE The transaction sequence for accessing the DS18B20 is as follows: Step 1. Initialization Step 2. ROM Command (followed by any required data exchange) Step 3. DS18B20 Function Command (followed by any required data exchange) It is very important to follow this sequence every time the DS18B20 is accessed, as the DS18B20 will not respond if any steps in the sequence are missing or out of order. Exceptions to this rule are the Search ROM [F0h] and Alarm Search [ECh] commands.
PAGE 10
DS18B20 SKIP ROM [CCh] The master can use this command to address all devices on the bus simultaneously without sending out any ROM code information. For example, the master can make all DS18B20s on the bus perform simultaneous temperature conversions by issuing a Skip ROM command followed by a Convert T [44h] command. Note, however, that the Skip ROM command can only be followed by the Read Scratchpad [BEh] command when there is one slave on the bus.
PAGE 11
DS18B20 is issued the master must enable a strong pullup on the 1-wire bus for at least 10 ms as described in the POWERING THE DS18B20 section. RECALL E2 [B8h] This command recalls the alarm trigger values (TH and TL) and configuration data from EEPROM and places the data in bytes 2, 3, and 4, respectively, in the scratchpad memory.
PAGE 12
DS18B20 ROM COMMANDS FLOW CHART Figure 11 Initialization Sequence MASTER TX RESET PULSE DS18B20 TX PRESENCE PULSE MASTER TX ROM COMMAND 33h READ ROM COMMAND Y N 55h MATCH ROM COMMAND F0h SEARCH ROM COMMAND N Y Y N ECh ALARM SEARCH COMMAND N Y Y MASTER TX BIT 0 DS18B20 TX BIT 0 DS18B20 TX BIT 0 DS18B20 TX BIT 0 DS18B20 TX BIT 0 MASTER TX BIT 0 MASTER TX BIT 0 BIT 0 MATCH? DEVICE(S) WITH ALARM FLAG SET? DS18B20 TX FAMILY CODE 1 BYTE N BIT 0 MATCH? DS18B20 TX SERIAL NUMBER 6 BYTES
PAGE 13
DS18B20 DS18B20 FUNCTION COMMANDS FLOW CHART Figure 12 44h CONVERT TEMPERATURE ? MASTER TX FUNCTION COMMAND 48h COPY SCRATCHPAD ? N Y Y N PARASITE POWER ? DS18B20 BEGINS CONVERSION Y N DATA COPIED FROM SCRATCHPAD TO EEPROM B4h READ POWER SUPPLY ? PARASITE POWERED ? N MASTER DISABLES STRONG PULLUP Y MASTER RX “0s” MASTER RX “1s” N B8h RECALL E2 ? MASTER RX “1s” BEh READ SCRATCHPAD ? N Y Y N COPY IN PROGRESS ? MASTER DISABLES STRONG PULLUP MASTER RX “0s” Y MASTER ENABLES STRONG
PAGE 14
DS18B20 1-WIRE SIGNALING The DS18B20 uses a strict 1-wire communication protocol to insure data integrity. Several signal types are defined by this protocol: reset pulse, presence pulse, write 0, write 1, read 0, and read 1. All of these signals, with the exception of the presence pulse, are initiated by the bus master.
PAGE 15
DS18B20 The DS18B20 samples the 1-wire bus during a window that lasts from 15 µs to 60 µs after the master initiates the write time slot. If the bus is high during the sampling window, a 1 is written to the DS18B20. If the line is low, a 0 is written to the DS18B20.
PAGE 16
DS18B20 Therefore, the master must release the bus and then sample the bus state within 15 µs from the start of the slot. Figure 15 illustrates that the sum of TINIT, TRC, and TSAMPLE must be less than 15 µs for a read time slot. Figure 16 shows that system timing margin is maximized by keeping TINIT and TRC as short as possible and by locating the master sample time during read time slots towards the end of the 15 µs period.
PAGE 17
DS18B20 DS18B20 OPERATION EXAMPLE 1 In this example there are multiple DS18B20s on the bus and they are using parasite power. The bus master initiates a temperature conversion in a specific DS18B20 and then reads its scratchpad and recalculates the CRC to verify the data. MASTER MODE TX RX TX TX TX TX TX RX TX TX TX RX DATA (LSB FIRST) Reset Presence 55h 64-bit ROM code 44h DQ line held high by strong pullup Reset Presence 55h 64-bit ROM code BEh 9 data bytes COMMENTS Master issues reset pulse.
PAGE 18
DS18B20 ABSOLUTE MAXIMUM RATINGS* Voltage on any pin relative to ground Operating temperature Storage temperature Soldering temperature –0.5V to +6.0V –55°C to +125°C –55°C to +125°C See J-STD-020A Specification *These are stress ratings only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability.
PAGE 19
DS18B20 AC ELECTRICAL CHARACTERISTICS: NV MEMORY (-55°C to +100°C; VDD=3.0V to 5.
PAGE 20
DS18B20 TIMING DIAGRAMS Figure 18 20 of 20