The DS18B20 digital thermometer provides 9-bit to  12-bit Celsius temperature measurements and has an  alarm function with nonvolatile user- programmable  upper and lower trigger points. The DS18B20  communicates over a 1-Wire bus that by definition  requires only one data line (and ground) for  communication with a central microprocessor. It has  an operating temperature range of -55°C to +125°C  and is accurate to ±0.4°C over the range of -10°C to  +70°C. In addition, the DS18B20 can derive power  directly from the data line (“parasite power”),  eliminating the need for an external power supply. Each DS18B20 has a unique 64-bit serial code,  which allows multiple DS18B20s to function on the  same 1-Wire bus. Thus, it is simple to use one  microprocessor to control many DS18B20s  distributed over a large area. Applications that can  benefit from this feature include HVAC  environmental controls, temperature monitoring  systems inside buildings, equipment, or machinery,  and process monitoring and control systems.