Elevating embedded systems with I3C

In modern electronics, embedded systems have become increasingly complex, incorporating a variety of sensors and components in many applications including IoT, computing, wearables and security-sensitive applications. To meet the growing requirements of these markets, the MIPI Alliance has developed the improved inter-integrated circuit (I3C) interface.

I3C is an advanced serial communication interface that offers a major upgrade in how electronic components can communicate with each other by providing faster communication rates, lower power consumption, and improved design flexibility. As a key component of an embedded system, microcontrollers (MCUs) are used to control application functions like sensor signal acquisition and closed-loop control.

We will delve into several applications that can utilize an MCU with an I3C communication interface, offering a robust upgrade path and compatibility for I²C and SPI implementations. 

I3C and IoT applications

IoT touches nearly every facet of our daily routines, spanning from household gadgets to sophisticated building automation and wearable devices. These interconnected devices gather and exchange data, fundamentally shaping our digital ecosystem. Within IoT devices, different types of sensors play a pivotal role, measuring, monitoring, and relaying crucial physical attributes like temperature, humidity, pressure, and distance, among others.

The I3C protocol offers several benefits for networked sensor nodes. It enables high-speed communication, with speeds of up to 12.5 MHz in single data rate (SDR) mode. It also supports in-band interrupts and dynamic addressing. In dynamic addressing, a central controller assigns unique addresses to each connected device, preventing address conflicts.

Compared to its predecessor I²C, I3C boasts faster speeds, a simpler 2-wire interface, a more efficient protocol structure, and operates at lower voltages to reduce power consumption. These improvements make I3C well-suited for efficiently managing multiple sensor nodes within a connected network.

Incorporating a low cost MCU with built-in I3C peripherals into IoT sensor nodes as an analog “aggregator” can enhance functionality and efficiency of the entire sensor network. In this setup, the MCU’s on-chip analog-to-digital converter (ADC) is utilized to convert readings from multiple analog sensors into digital values.

These digital values can then be stored in the MCU’s internal memory for further analysis or organized for more efficient transmission. The aggregated sensor data is transmitted to the main controller via the I3C bus at intervals optimized for system efficiency.

The distinct advantage of I3C in sensor-based systems becomes apparent when considering its capacity to minimize component complexity, cost, and power consumption by necessitating fewer pins and wires compared to alternative communication interfaces.

For system designers navigating the demanding IoT market landscape, a compact MCU with I3C communication interface emerges as an essential solution, facilitating the creation of successful IoT devices that align with market requirements.

Multiple protocols and multiple voltages in embedded devices

As technology requirements grow, embedded developers face increasing challenges with backward compatibility. This compatibility is crucial because it allows for embedded systems to be gradually updated, rather than completely redesigned. To help ease the transition to I3C, the new communication protocol addresses the limitations of I²C and SMBus, while using the same two pins as I²C for clock and data to maintain compatibility.

While I3C aims to be backward-compatible with I²C/SMBus protocols, the presence of an I²C/SMBus device on an I3C bus can affect bus performance, even with controller optimization for I3C devices. To resolve this, an MCU with an I3C module can serve as a bridge device, isolating I²C/SMBus target devices from the “pure” I3C bus.

This maintains the integrity of the I3C bus, allowing the main I3C controller to communicate with I²C /SPI devices via the bridge MCU. Additionally, the MCU can consolidate interrupts from I²C /SMBus devices and transmit them to the main I3C controller using in-band interrupts, without additional pins or signals.

Embedded systems incorporate various components such as MCUs, sensors, and other circuits. Oftentimes, these components need to be connected to one another, yet they operate in different voltage domains. For instance, analog sensors typically operate at 5 V, while communication protocols like I²C and SMBus require 3.3 V. The I3C bus can even operate at 1 V to match the requirements of modern high-speed processors.

MCUs with a multi-voltage I/O (MVIO) feature resolve voltage incompatibility and eliminate the need for level shifters. This feature enables I3C and I²C /SMBus buses to operate at different voltages simultaneously. For instance, an MCU can run the I3C bus at 1 V while keeping the I²C /SMBus bus at a higher 3.3 V for compatibility with legacy devices.

As shown in Figure 1, Microchip’s PIC18-Q20 MCUs, with MVIO support, offer multiple communication protocols like I3C, SPI, I²C, and UART, and up to three independent operating voltage domains. This flexibility proves highly beneficial in complex networked environments where devices use different protocols and voltages, allowing embedded developers to maintain existing protocols while futureproofing their designs.

Figure 1 The PIC18-Q20 MCUs, with MVIO support, offer multiple communication protocols like I3C, SPI, I²C, and UART, and up to three independent operating voltage domains. This offers flexibility in networked environments where embedded devices may use different protocols and voltages. Source: Microchip

Modern computing infrastructure

People can easily underestimate how much we rely on data centers in our daily digital lives. From conducting business and financial transactions to browsing the internet, storing data, engaging in social networking, attending virtual meetings, and enjoying digital entertainment—all these activities are facilitated by data centers. These centers ensure that our data is safe, our internet is fast, and our digital services are always available.

At the core of the data center lies the modern blade server: a highly advanced computer designed to maximize space efficiency and optimize network performance on a large scale. Due to the crucial nature of their function, certain system tasks within each server chassis are delegated to a sideband controller.

While the main processing unit focuses on managing the primary data flow, the sideband controller steps in to enhance network performance. It establishes a secondary communication channel to oversee individual server blades and handles important tasks such as monitoring system health, detecting faults, discovering and configuring devices, updating firmware, and conducting diagnostics without disrupting the main processor.

This ensures smooth and efficient operation. Sideband management serves as a critical tool that can greatly enhance the reliability, availability and efficiency of data centers.

Solid state drives (SSDs) are also commonly used in data centers to store and quickly access data. The newest SSD form factor, SNIA Enterprise and Datacenter Standard Form Factor (EDSFF), has adopted the I3C protocol for sideband communication as a natural upgrade from the existing SMBus protocol.

I3C addresses the demand for faster performance, higher data transfer rates, and improved power efficiency. The high-speed communication of I3C enables faster bus management and configuration modifications for enhanced system responsiveness.

Flexible MCUs such as the PIC18-Q20 family (Figure 2) are particularly well-suited for system management tasks in data center and enterprise environments. With up to two separate I3C interfaces, these MCUs can easily connect to an SSD controller for performing system management tasks, as well as to a baseboard management controller (BMC) via a sideband connection.

Figure 2: The PIC18-Q20 family will easily connect to an SSD and BMC controller via a sideband connection. Source: Microchip

Moreover, with built-in legacy communication protocols like I²C/SMBus, SPI, and UART, these devices represent an ideal solution for both current and next-generation SSD designs.

I3C’s growing ubiquity

The integration of the I3C protocol has emerged as an enabling force in embedded systems. The enhanced communication capabilities, lower power consumption, and compatibility with existing protocols make I3C a cornerstone for next-generation IoT and computing applications.

By optimizing sensor functionalities in IoT devices and data center communication, the versatility of I3C when integrated into MCUs can provide a robust foundation for the modern electronic systems. The adoption of I3C is quickly growing in ubiquity, enabling enhanced performance, reliability, and efficiency.

Stephanie Pinteric and Ulises Iniguez are senior product marketing engineers in Microchip’s 8-bit MCU business unit.

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