1 of 20 061002FEATURES§ Unique 1-Wire® interface requires only oneport pin for communication.§ Each device has a unique 64-bit serial codestored in an on-board ROM.§ Multidrop capability simplifies distributedtemperature-sensing applications.§ Requires no external components.§ Can be powered from data line. Power supplyrange is 3.0V to 5.5V.§ Measures temperatures from -55°C to +125°C(-67°F to +257°F).§ ±2.0°C accuracy from -10°C to +85°C.§ Thermometer resolution is user-selectablefrom 9 to 12 bits.§ Converts temperature to 12-bit digital word in750ms (max.)§ User-definable nonvolatile (NV) alarmsettings.§ Alarm search command identifies andaddresses devices whose temperature isoutside of programmed limits (temperaturealarm condition).§ Software compatible with the DS18B20.§ Applications include thermostatic controls,industrial systems, consumer products,thermometers, or any thermally sensitivesystem.PIN ASSIGNMENTPIN DESCRIPTIONGND - GroundDQ - Data In/OutVDD- Power Supply VoltageNC - No ConnectDESCRIPTIONThe DS1822 digital thermometer provides 9- to 12-bit centigrade temperature measurements and has analarm function with NV user-programmable upper and lower trigger points. The DS1822 communicatesover a 1-Wire bus that by definition requires only one data line (and ground) for communication with acentral microprocessor. It has an operating temperature range of –55°C to +125°C and is accurate to±2.0°C over the range of –10°C to +85°C. In addition, the DS1822 can derive power directly from thedata line (“parasite power”), eliminating the need for an external power supply.Each DS1822 has a unique 64-bit serial code, which allows multiple DS1822s to function on the 1-Wirebus; thus, it is simple to use one microprocessor to control many DS1822s distributed over a large area.Applications that can benefit from this feature include HVAC environmental controls, temperaturemonitoring systems inside buildings, equipment or machinery, and process monitoring and controlsystems.1 (BOTTOM VIEW)2 3 DS1822Econo 1-Wire DigitalThermometerwww.maxim-ic.com8-Pin 150mil SO(DS1822Z)TO-92(DS1822)DALLAS18221GNDDQVDD23NCNCNCNCGNDDQVDDNC68753124DS18221-Wire is a registered trademark of Dallas Semiconductor.DS18222 of 20DETAILED PIN DESCRIPTIONS Table 18-PIN SO* TO-92 SYMBOL DESCRIPTION5 1 GNDGround.42DQData Input/Output pin. Open-drain 1-Wire interface pin. Alsoprovides power to the device when used in parasite power mode(see “Parasite Power” section).33VDDOptional VDD pin. VDD must be grounded for operation inparasite power mode.*All pins not specified in this table are “No Connect” pins.OVERVIEWFigure 1 shows a block diagram of the DS1822, and pin descriptions are given in Table 1. The 64-bitROM stores the device’s unique serial code. The scratchpad memory contains the 2-byte temperatureregister that stores the digital output from the temperature sensor. In addition, the scratchpad providesaccess to the 1-byte upper and lower alarm trigger registers (TH and TL), and the 1-byte configurationregister. The configuration register allows the user to set the resolution of the temperature-to-digitalconversion to 9, 10, 11, or 12 bits. The TH, TL and configuration registers are NV (EEPROM), so they willretain data when the device is powered down.The DS1822 uses Dallas’ exclusive 1-Wire bus protocol that implements bus communication using onecontrol signal. The control line requires a weak pullup resistor since all devices are linked to the bus via a3-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 isvirtually unlimited. The 1-Wire bus protocol, including detailed explanations of the commands and “timeslots,” 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 insteadsupplied through the 1-Wire pullup resistor via the DQ pin when the bus is high. The high bus signal alsocharges an internal capacitor (CPP), which then supplies power to the device when the bus is low. Thismethod of deriving power from the 1-Wire bus is referred to as “parasite power.” As an alternative, theDS1822 may also be powered by an external supply on VDD.DS1822 BLOCK DIAGRAM Figure 1VPU4.7KPOWERSUPPLYSENSE64-BIT ROMAND 1-wire PORTDQVDDINTERNAL VDDCPPPARASITE POWERCIRCUITMEMORY CONTROLLOGICSCRATCHPAD8-BIT CRC GENERATORTEMPERATURE SENSORALARM HIGH TRIGGER (TH)REGISTER (EEPROM)ALARM LOW TRIGGER (TL)REGISTER (EEPROM)CONFIGURATION REGISTER(EEPROM)GNDDS1822DS18223 of 20OPERATION—MEASURING TEMPERATUREThe core functionality of the DS1822 is its direct-to-digital temperature sensor. The resolution of thetemperature 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 DS1822powers-up in a low-power idle state; to initiate a temperature measurement and A-to-D conversion, themaster must issue a Convert T [44h] command. Following the conversion, the resulting thermal data isstored in the 2-byte temperature register in the scratchpad memory and the DS1822 returns to its idlestate. If the DS1822 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 DS1822 will respond bytransmitting 0 while the temperature conversion is in progress and 1 when the conversion is done. If theDS1822 is powered with parasite power, this notification technique cannot be used since the bus must bepulled high by a strong pullup during the entire temperature conversion. The bus requirements for parasitepower are explained in detail in the POWERING THE DS1822 section of this data sheet.The DS1822 output temperature data is calibrated in degrees centigrade; for Fahrenheit applications, alookup table or conversion routine must be used. The temperature data is stored as a 16-bit sign-extendedtwo’s complement number in the temperature register (see Figure 2). The sign bits (S) indicate if thetemperature is positive or negative: for positive numbers S = 0 and for negative numbers S = 1. If theDS1822 is configured for 12-bit
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