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Tuesday, August 02, 2016

Say hello to the new I3C interface

By Nick Flaherty

Following on from the well established I2C interface standard, I3C is about to hit the embedded market.

The standard, developed by the MIPI consortium and now extending out to the wider market, combines I2C, UART and SPI into a 10Mbit/s, low power specification for designers with new features such as support for interrupts, hot swapping and multiple sensors.

However, it will take a little bit of time for the 2000 gates in the IP to be designed into devices, so it will be backwards compatible with 'most types' of I2C device and, importantly, the new devices will work on existing I2C busses.

The new approach makes it easier for both device manufacturers and software developers to add more sensors to devices and combine multiple sensors from different vendors in products while reducing component and implementation costs. The specification also improves performance and power efficiency and provides sensor management capabilities not previously available.

“MIPI I3C was developed with tremendous collaboration and dedication from companies across the mobile, sensor and other industries who share common goals for innovation,” said Ken Foust, chair of the MIPI Alliance Sensor Working Group. “The contributions of so many stakeholders underscore the interest, need and demand in the marketplace for a new solution.”

Like I2C, it uses a 2-wire interface (compared to the 4-wire SPI), which drastically reduces pin count and signal paths and facilitates incorporation of more sensors in a device. MIPI I3C can also be used as a sideband interface to other high-speed interfaces, a function previously provided by I2C and SPI, to further reduce pin count.

On a standard CMOS I/O, MIPI I3C supports a minimum data rate of 10 Mbps with options for high-data-rate modes, offering a substantial leap in performance and power efficiency compared to previous options. It uses one-eighth the power compared to I2C, for example, while providing 100 times the bandwidth.
Support for In-Band Interrupt (IBI) enables the devices present on the 2-wire MIPI I3C bus to issue interrupts without using extra I/O pins signals. The I2C and SPI interfaces typically require out-of-band signals to implement interrupt functionality.

The new standard provides synchronous and asynchronous time stamping to improve the accuracy of applications that use signals from various sensors over time. The time control improves the coordination of individual sensors, such as gyros and accelerometers, enabling them to work better together while substantially decreasing the energy required to operate the various devices.

This means sensors can work in an always-on manner, even if other components in a device are asleep, while operating at very low power to minimize impact on battery life. It enables always-on sensors to accumulate (batch) data and transmit it quickly, when needed, to minimize energy consumption.

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