DS1822

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DETAILED PIN DESCRIPTIONS Table 1

8-PIN SO*

TO-92 SYMBOL DESCRIPTION

5

1

GND

Ground.

42

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).

33

parasite power mode.

*All pins not specified in this table are “No Connect” pins.

OVERVIEW

Figure 1 shows a block diagram of the DS1822, 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 provides

register. The configuration register allows the user to set the resolution of the temperature-to-digital

retain data when the device is powered down.

The DS1822 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). 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.

Another feature of the DS1822 is the 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 high bus signal also

method of deriving power from the 1-Wire bus is referred to as “parasite power.” As an alternative, the

DS1822 BLOCK DIAGRAM Figure 1

4.7K

POWER

SUPPLY

SENSE

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