RTC or real-time clock is a kind of computer clock for keeping track of the recent or most current time. Commonly, RTCs are present in almost all or any device, which are electronic in nature that needs to keep time accurate. Meanwhile, temperature sensors are devices that gather data concerning the temperature from a source and convert it to a form that can be understood either by an observer or another device. These sensors can be in various forms and are used for a wide variety of purposes, from simple home use to extremely accurate and precise scientific use. They play a very important role almost everywhere that they are applied; knowing the temperature helps people to pick their clothing before a walk outside just as it helps chemists to understand the data collected from a complex chemical reaction.
The circuit uses a PCA8565 CMOS real time clock and calendar optimized for low power consumption. A programmable clock output, interrupt output and voltage-low detector are also provided. All address and data are transferred serially via a two-line bidirectional I2C-bus with a maximum bus speed of 400kbit/s. The built-in word address register is incremented automatically after each written or read data byte. It also includes a MCP9801 digital temperature sensor capable of reading temperatures from -55°C to +125°C. Temperature data is measured from an integrated temperature sensor and converted to digital word with a user selectable 9 to 12 bit Sigma Delta Analog to Digital Converter. The MCP9801 notifies the host controller when the ambient temperature exceeds a user programmed set point. The ALERT output is programmable as either a simple comparator for thermostat operation or as a temperature event interrupts. Communication with the sensor is accomplished via a two-wire bus that is compatible with industry standard protocols. This permits reading the current temperature, programming the set point and hysteresis and configuring the device. Address selection inputs allow up to eight MCP9801 sensors to share the same two-wire bus for multizone monitoring. Small physical size, low installed cost and ease of use make the MCP9801 an ideal choice for implementing sophisticated temperature system management schemes in a variety of applications.
For more detail: I2C Temperature Sensor & Real Time Clock