The I3C protocol (also known as MIPI I3C) stands for "Improved Inter-Integrated Circuit" and is a communication
interface standard developed by the MIPI Alliance, a consortium of companies in the mobile industry.
I3C is an evolution of the I2C (Inter-Integrated Circuit) protocol, which is widely used for communication between
integrated circuits. However, I3C offers several improvements over I2C, including higher data transfer rates, lower
power consumption, and improved support for various device types.
Some key features of I3C include:

High-speed data transfer: I3C supports data transfer rates of up to 33.33 Mbps, which is significantly faster than
the 1 Mbps supported by I2C.

Backward compatibility with I2C: I3C devices can communicate with I2C devices, which helps to facilitate the
transition to the new protocol.

Dynamic address assignment: I3C devices can automatically assign addresses to themselves, which reduces the
need for manual configuration.

Multi-master support: I3C supports multiple masters on the same bus, which allows for more flexible system
designs.

Improved power management: I3C includes features such as clock stretching and sleep modes that help to
reduce power consumption.
Overall, the I3C protocol is designed to provide a more efficient and flexible communication interface for various types
of integrated circuits, particularly in the mobile industry.
I3C has also introduced new features such as in-band interrupts, hot-join support, and a standardized discovery
mechanism. These features help to simplify system design and improve the reliability and performance of I3C devices.
In-band interrupts allow I3C devices to send interrupts to the master using the same data line as the normal data
communication, eliminating the need for a separate interrupt line. This reduces the number of pins required for
communication, which can be particularly beneficial in mobile devices with limited space.
Hot-join support allows I3C devices to be added or removed from the bus dynamically, without requiring a system reset
or reconfiguration. This can be useful in situations where devices need to be swapped out or added to the system
without interrupting operation.
Finally, the standardized discovery mechanism in I3C allows devices to advertise their capabilities and features to the
master, simplifying the process of identifying and configuring devices on the bus.
In summary, the I3C protocol offers a number of improvements over the previous I2C protocol, including faster data
transfer rates, improved power management, and support for a wider range of device types. These features make I3C an
attractive option for communication between integrated circuits, particularly in the mobile industry where space and
power constraints are often critical considerations.
To achieve these improvements, I3C combines elements from I2C, Serial Peripheral Interface (SPI), and System
Management Bus (SMBus) protocols. This allows I3C to leverage the benefits of each protocol while minimizing their
limitations.
I3C achieves higher data transfer rates by using a high-speed mode that supports clock rates up to 12.5 MHz. It also uses
a new data format that allows data to be transmitted and received simultaneously, reducing the number of bus cycles
required for communication.
In addition, I3C introduces a new device identification mechanism that uses a 7-bit address space with a 1-bit extension.
This allows for up to 112 unique device addresses, which is a significant increase over the 127 addresses supported by
I2C. The extension bit also enables support for multi-drop devices, where multiple devices can share the same physical
address.
Another key feature of I3C is its support for advanced power management. This includes features such as clock
stretching, where a device can hold the clock line low to indicate that it is not ready to transmit data. I3C also supports
low-power modes that allow devices to enter a sleep state when not in use, reducing power consumption.
Overall, the I3C protocol offers significant improvements over I2C, particularly in terms of data transfer rates and power
management. Its support for advanced features such as in-band interrupts and hot-join makes it a more flexible and
versatile protocol for communication between integrated circuits.
I3C also includes a mechanism for device discovery and enumeration, which is achieved through the use of the Dynamic
Address Assignment (DAA) protocol. DAA allows I3C devices to automatically assign themselves addresses on the bus,
eliminating the need for manual address configuration.
In addition to DAA, I3C also introduces a standardized discovery mechanism called the Discovery and Configuration
(DaC) protocol. DaC allows devices to advertise their capabilities and features to the master, making it easier for the
master to identify and configure devices on the bus. This can be particularly useful in systems with a large number of I3C
devices or in situations where device capabilities may change over time.
I3C also includes support for multi-master operation, where multiple masters can communicate with the same set of
slaves. This is achieved through the use of arbitration and priority mechanisms that allow the bus to be shared between
multiple masters.
Finally, I3C introduces support for advanced features such as In-band interrupts, which allow I3C devices to send
interrupts to the master using the same data line as normal data communication, and Hot-join support, which allows
devices to be added or removed from the bus dynamically without requiring a system reset or reconfiguration.
Overall, the I3C protocol offers significant improvements over I2C in terms of performance, flexibility, and power
management. Its support for advanced features and device discovery mechanisms makes it a more versatile protocol for
communication between integrated circuits, particularly in the mobile and Internet of Things (IoT) industries.
SMBus stands for System Management Bus, which is a two-wire communication protocol used for low-speed
communication between devices in a computer system. SMBus is derived from the I2C protocol and is backwardcompatible with I2C devices, but it includes additional specifications for system management functions.
SMBus was originally developed by Intel Corporation in 1995 as a way to monitor and manage system hardware
components such as temperature sensors, voltage regulators, and fan controllers. Today, SMBus is used for a wide range
of system management tasks, including power management, system monitoring, and firmware updates.
SMBus operates over a two-wire serial bus, which consists of a clock line (SCL) and a data line (SDA). Communication is
initiated by the master device, which sends a start condition followed by a slave address and a read or write bit. The
slave device then responds with an acknowledge (ACK) or no-acknowledge (NACK) signal, depending on whether it is
able to receive data or not.
SMBus defines a number of standard commands for system management tasks, including commands for reading and
writing data, controlling device functions, and querying device capabilities. SMBus also includes specifications for
addressing, clock synchronization, and error checking to ensure reliable communication between devices.
One of the key advantages of SMBus is its simplicity and low cost. Because SMBus uses a two-wire interface and
operates at low speeds, it can be implemented using simple hardware and does not require high-performance
microcontrollers. This makes it an attractive option for system management tasks in low-cost and low-power devices.
Overall, SMBus is a simple and cost-effective protocol for system management tasks, offering backward compatibility
with I2C devices and support for a wide range of system management functions.
SMBus also includes a number of features for power management, including support for device power states and the
ability to control device power consumption. For example, an SMBus controller can put a device into a low-power sleep
state when it is not being used, or it can adjust the voltage or frequency of a device to reduce power consumption.
In addition, SMBus supports a number of alert mechanisms for system monitoring and management. For example, an
SMBus-enabled temperature sensor can send an alert to the system if the temperature exceeds a certain threshold,
allowing the system to take action to prevent damage or failure.
SMBus is widely used in desktop and laptop computers, as well as in embedded systems and other electronic devices. Its
simple and cost-effective design make it well-suited for a variety of system management tasks, and its compatibility with
I2C devices makes it easy to integrate with existing hardware and software designs.
However, SMBus has some limitations compared to other communication protocols. For example, its maximum data
transfer rate is limited to 100 kbit/s, which can be a bottleneck for some applications. Additionally, SMBus does not
support advanced features such as multi-master operation or hot-join, which can limit its flexibility in larger systems.
Overall, SMBus is a useful protocol for system management tasks in low-cost and low-power devices, offering a simple
and cost-effective solution for system monitoring and control. However, for more demanding applications, other
protocols such as I2C or I3C may offer better performance and features.