The DS1621 Digital Thermometer and Thermostat provides 9bit temperature readings which indicate the temperature of the device. The thermal alarm output, TOUT, is active when the temperature of the device exceeds a userdefined temperature TH. The output remains active until the temperature drops below user defined temperature TL, allowing for any hysteresis necessary. User-defined temperature settings are stored in nonvolatile memory so parts may be programmed prior to insertion in a system. Temperature settings and temperature readings are all communicated to/from the DS1621 over a simple twowire serial interface.