DS1822-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 DS1822-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 DS1822-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 data sheet.

An important feature of the DS1822-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 DS1822-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

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

DS1822-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

DS1822-PAR