Direct-to-digital temperature sensor from Dallas Semiconductor can be multidropped for distributed temperature measurement; Draws all power needed from the data line.

DALLAS--(BUSINESS WIRE)--Oct. 17, 1995--Dallas Semiconductor (NYSE:DS) Tuesday announced the first direct-to-digital temperature sensor that can be multidropped.

Multiple DS1820 1-Wire Digital Thermometers can be placed on a single twisted pair wire, eliminating the complexity and dramatically reducing the expense of distributed temperature measurement.

Multidrop capability simplifies distributed temperature sensing applications, whether the task is to measure temperature inside an electronics enclosure or in a building. Multidrop capability is made possible by the fact that each DS1820 has a guaranteed-unique serial number etched in silicon.

Using this 64-bit lasered ROM, the Dallas proprietary 1-Wire protocol can identify the temperature of a specific sensor. Thus multiple chips residing on a 1-Wire bus can report back to a central processor, eliminating the need for separate wiring for each temperature sensor. 1-Wire signals can travel for a distance of 300 meters.

Rick Downs, product manager, said: "The DS1820 provides 9-bit temperature readings. Only one wire (plus ground) needs to be connected from a central microprocessor to a DS1820 to send information back and forth. A worker can stand at the host station and read temperature remotely. This solution gets rid of a lot of the analog circuitry and it reduces the need for shielded cable."

Applications where this feature is useful include HVAC environmental controls, sensing temperature inside buildings, equipment or machinery, and process monitoring and control.

The DS1820 measures temperatures from -55 C to +125 C in 0.5 C increments. Fahrenheit equivalent is -67 F to 257 F in 0.9 F increments. It converts temperature to a digital word in 200 ms (typical).

Downs said: "In 1993, Dallas Semiconductor introduced the DS1620 Digital Thermometer, the first temperature sensor to directly output a digital number. Like its predecessor, the DS1820 requires no external components and no A/D conversion. The signal traveling down the twisted pair wire is clean because it's digital -- there are no analog signals traveling to the host computer to pick up noise along the way."

As a special energy-conservation feature, the DS1820 requires zero standby power. Further, power for reading, writing, and performing temperature conversions can be derived from the data line itself with no need for an external power source. The device stores energy on an internal capacitor during periods when the signal line is high and continues to operate off this power source during the low times of the 1-Wire line until it returns high to replenish the capacitor supply.

In order to ensure that temperatures stay within the required range, the DS1820 features a user-definable, nonvolatile temperature alarm setting. An alarm search command identifies and addresses devices whose temperature is outside of programmed limits so the user can take action to adjust the temperature.

The DS1820 1-Wire Digital Thermometer is available in a 3-lead device that saves pin count or as a 16-pin SSOP for surface-mount applications. Currently available from stock, the DS1820 in the 3-pin package costs $2.77 in quantities of 10,000.

Dallas Semiconductor designs, manufactures and markets CMOS chips and chip-based subsystems. In its 11-year history, the company has sold its products to more than 8,000 customers worldwide. These include Original Equipment Manufacturers (OEMs) in instrumentation, factory automation, personal computers, office equipment, telecommunications, medical equipment, and mainframe computers. Chips and subsystems are sold through a direct sales force, distributors and manufacturers' representatives worldwide.

CONTACT: Dallas Semiconductor

Rick Downs, 214/450-0448

214/450-0470 (fax)

or

Syd Coppersmith, 214/450-5349