DS18B20-PAR

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DETAILED PIN DESCRIPTIONS Table 1

PIN

SYMBOL

DESCRIPTION

1

GND

Ground.

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

NC

No Connect. Doesn’t connect to internal circuit.

OVERVIEW

The DS18B20-PAR uses Dallas’ exclusive 1-Wire bus protocol that implements bus communication

using one control signal. The control line requires a weak pullup resistor since all devices are linked to

the bus via a 3-state or open-drain port (the DQ pin in the case of the DS18B20-PAR). In this bus

system, the microprocessor (the master device) identifies and addresses devices on the bus using each

device’s unique 64-bit code. Because each device has a unique code, the number of devices that can be

addressed on one bus is virtually unlimited. The 1-Wire bus protocol, including detailed explanations of

the commands and “time slots,” is covered in the 1-WIRE BUS SYSTEM section of this datasheet.

An important feature of the DS18B20-PAR is its ability to operate without an external power supply.

Power is instead supplied through the 1-Wire pullup resistor via the DQ pin when the bus is high. The

bus is low. This method of deriving power from the 1-Wire bus is referred to as “parasite power.”

Figure 1 shows a block diagram of the DS18B20-PAR, and pin descriptions are given in Table 1. The

64-bit ROM stores the device’s unique serial code. The scratchpad memory contains the 2-byte

temperature register that stores the digital output from the temperature sensor. In addition, the scratchpad

registers are nonvolatile (EEPROM), so they will retain their data when the device is powered down.

DS18B20-PAR BLOCK DIAGRAM Figure 1

4.7K

64-BIT ROM

AND

1-wire PORT

DQ

PARASITE POWER

CIRCUIT

MEMORY CONTROL

LOGIC

SCRATCHPAD

8-BIT CRC GENERATOR

TEMPERATURE SENSOR

REGISTER (EEPROM)

REGISTER (EEPROM)

CONFIGURATION REGISTER

(EEPROM)

GND

DS18B20-PAR