Two types of measurement modes are available on the HDC302x: Trigger-on Demand and Auto Measurement mode.
Trigger-on Demand is a single measurement reading of temperature and relative humidity that is triggered through an I2C command on an as-needed basis. After the measurement is converted, the device remains in sleep mode until another I2C command is received.
Auto Measurement mode is a recurring measurement reading of temperature and relative humidity, eliminating the need to repeatedly initiate a measurement request through an I2C command. The measurement interval can be adjusted from 1 measurement every 2 seconds to 10 measurements every second. In Auto Measurement mode, the HDC302x wakes up from sleep to measurement mode based on the selected sampling rate.
Auto Measurement mode helps to reduce overall system power consumption in two ways. First, by removing the need to repeatedly initiate a measurement through an I2C command, sink current through the SCL and SDA pullup resistors is eliminated. Secondly, a microcontroller can be programmed into a deep sleep mode, and only woken up through an interrupt by the ALERT pin in the event of excessive temperature and relative humidity measurements.