What are Serial Communication Protocols? - ECE-180D-WS-2024/Wiki-Knowledge-Base GitHub Wiki

What is serial communication?

In today's interconnected world, where devices seamlessly communicate with each other, serial communication emerges as the silent yet vital conductor orchestrating the symphony of digital interactions. Serial communication is a method of transmitting data between two or more devices over a serial interface, where data is sent one bit at a time sequentially over a single communication line. It is a means to communicate between transmitting and receiving devices either physically through wires or wirelessly. While it can be done in either way, the transmission of data remains the same sequentially, one bit at a time, over a communication channel. In this article we will be going over SPI, I2C, and UART communication protocols and the advantages/disadvantages to them.

Synchronous vs. Asynchronous Communication

Under the umbrella of serial communication there are two primary forms on how the timing of data gets transmitted. Synchronous and asynchronous communication. Synchronous communication is when data is governed by a shared clock and allows the devices that are interfacing with each other to send and receive data when the clock signal arrives. Asynchronous communication is when the timing of when data gets transmitted between devices is not dependent on a clock. Each byte of data is framed by start and stop bits to differentiate the beginning and end of a piece of data.

Transmission Modes in Serial Communication

Transmission modes in serial communication refer to the direction of data flow between communicating devices. In serial communication there are three types of modes: Simplex Method, Half Duplex Method, Full Duplex Method. Simplex transmission is a one way direction of data transmission where one device only receives data and the other device only transmits data. Half Duplex transmission data can flow in both directions, but not simultaneously. Full Duplex transmission data devices can transmit and receive data simultaneously.

Common Serial Communication Protocols

Now that we've established what serial communication is and the two sub categories, we'll go into more detail how exactly each communication protocol works and the advantages and disadvantages.

SPI (Serial Peripheral Interface)

SPI communication falls under the category of full duplex transmission under synchronization with a clock. Data can flow simultaneously in both directions between the master and slave devices. This means that during SPI communication, the master device can transmit data to the slave devices on the MOSI (Master Out Slave In) line while receiving data from the slave device on the MISO (Master In Slave Out) line. The serial clock signal (SCK) generated by the master device synchronizes data transmission between the master and slave. It determines the rate at which data is transferred and ensures alignment between transmitted and received data. Each slave device is assigned a dedicated chip select (SS) line controlled by the master device. When the master selects a particular slave for communication, it asserts the corresponding chip select line to enable communication with that slave while keeping other slaves inactive. Advantages to SPI include high speed data transfer rates, simple implementation, and communication with multiple slave devices. Disadvantages are SPI usually only works over short distances and if you have multiple slaves this means having increased wiring complexity. Some components that use SPI are flash memory chips because the high-speed data transfer rates make it ideal for reading and writing data to flash memory chips in embedded systems. Display modules are also perfect for SPI because they enable fast refresh rates and smooth graphics rendering, in devices like smartphones, digital cameras, and portable gaming consoles. Ethernet controllers also used SPI in order to facilitate fast data exchange between the microcontroller and the network interface.

I2C (Inter-Integrated Circuit)

I2C is a synchronous, multi-master serial communication protocol designed for communication between integrated circuits. It utilizes a two-wire interface consisting of a serial data line (SDA) and a serial clock line (SCL), enabling bidirectional data transfer between multiple master and slave devices connected on the same bus. I2C operates in a half-duplex mode, allowing devices to transmit and receive data over the same communication lines simultaneously. The protocol supports multi-master operation, allowing multiple devices to initiate communication on the bus, and features addressable slave devices, enabling targeted communication with specific devices. I2C communication may suffer from slower data transfer rates compared to other protocols like SPI, limited distance due to signal degradation, and susceptibility to clock stretching issues, where slave devices temporarily hold the clock line low to slow down data transmission. However, a plus is that each slave device connected to the I2C bus is assigned a unique address, enabling targeted communication with specific devices. This addressing scheme facilitates efficient data exchange in multi-device configurations. Some components that use I2C are sensor networks allowing multiple sensors to communicate with a microcontroller over a shared bus. Real-time clock modules for timekeeping applications in electronic devices like digital watches, alarm clocks, and data loggers, providing accurate time information to the system. I2C is also utilized in EEPROM (Electrically Erasable Programmable Read-Only Memory) chips for storing configuration data and user settings in electronic devices, enabling easy read/write access via the I2C bus.

UART (Universal Asynchronous Receiver-Transmitter)

UART is a widely used asynchronous serial communication protocol that facilitates the transmission and reception of serial data between devices using only two wires: a transmit line (TX), sending data and a receive line (RX), receiving data. UART communication operates in a simplex or half-duplex mode, allowing data to flow in one direction at a time. Advantages of UART is its simplicity and versatility. However, UART communication may suffer from limited data transfer rates compared to synchronous protocols like SPI and I2C, making it less suitable for high-speed applications. Some components using UART are GPS modules, commonly used to interface with GPS modules in navigation systems, drones, and vehicle tracking devices, enabling the exchange of location data and navigation commands between the GPS receiver and the microcontroller. Bluetooth and Wi-Fi modules are also great candidates for UART, for establishing serial communication links between devices, enabling wireless data transfer and remote control functionalities.

Applications

This next section looks to outline the borad use of these communication protocols in industry. This section provides various examples for protocols uses and why that particluar protocol is used for that application as opposed to others.

SPI Applications

Automotive Industry: In automotive electronics, SPI is widely used for communication between various components such as engine control units (ECUs), dashboard displays, and sensors. SPI is preferred in this application due to its high-speed data transfer capability, precise synchronization, and straightforward implementation. These characteristics are essential for real-time control and monitoring of automotive systems, ensuring optimal engine performance and vehicle safety.
Industrial Automation: SPI is used in industrial automation systems where high-speed communication is essential for controlling machinery and monitoring processes. SPI is favored in industrial applications for its reliability, noise immunity, and ability to support multiple slave devices. These qualities make SPI suitable for harsh environments where robust communication is critical for maintaining operational efficiency and minimizing downtime.
Medical Devices: Used in various medical devices, SPI is implemented for data transmission between sensors, controllers, and display units. SPI is chosen for medical applications due to its low latency and compatibility with a wide range of sensors and actuators. These characteristics ensure accurate and timely data acquisition, contributing to the reliability and effectiveness of medical devices in patient monitoring and healthcare delivery.

I2C Applications

Smart Home Devices: I2C is prevalent in smart home devices such as thermostats, smart lighting systems, and security cameras. I2C is preferred in smart home applications for its simplicity, low power consumption, and support for multi-master communication. These features enable seamless integration of diverse devices within the smart home ecosystem, allowing for centralized control and automation of various functions while minimizing power consumption and system complexity.
Avionics: In aviation, I2C is employed in avionics systems for communication between flight control computers, navigation systems, and cockpit displays. I2C is selected for avionics applications due to its lightweight protocol overhead, deterministic communication, and compatibility with redundant communication channels. These characteristics are crucial for ensuring reliable and fault-tolerant communication in safety-critical aviation systems, contributing to the overall safety and efficiency of air transportation.
Consumer Electronics: I2C is extensively used in consumer electronics products like TVs, audio systems, and gaming consoles. I2C is preferred in consumer electronics applications for its ease of integration, low cost, and support for multi-device communication. These features enable manufacturers to design compact and cost-effective products with rich functionality, allowing for seamless interaction and interoperability among various consumer electronics devices.

UART Applications

Telecommunications: UART is commonly used in telecommunications equipment for serial communication between modems, routers, and network switches. UART is chosen for telecommunications applications due to its simplicity, universality, and compatibility with legacy communication standards. These characteristics make UART suitable for a wide range of communication interfaces, ensuring interoperability and backward compatibility in diverse telecommunication networks and equipment.
Automated Teller Machines (ATMs): UART plays a vital role in ATM systems for communication between the main control unit, card reader, cash dispenser, and receipt printer. UART is preferred in ATM applications for its reliability, real-time communication, and low hardware overhead. These characteristics ensure secure and efficient transaction processing in ATM systems, enabling seamless interaction between the ATM and the user while minimizing downtime and operational costs.
Industrial Control Systems: In industrial environments, UART is employed in control systems for communication between programmable logic controllers (PLCs), motor controllers, and human-machine interfaces (HMIs). UART is selected for industrial control applications due to its simplicity, robustness, and compatibility with legacy equipment. These characteristics make UART suitable for real-time monitoring and control of industrial processes, facilitating seamless integration and interoperability across diverse industrial automation systems.

These real-world examples demonstrate the diverse applications of SPI, I2C, and UART across various industries, highlighting their importance in enabling efficient and reliable communication between electronic devices and systems.

Conclusion

Serial communication serves as a fundamental method for transmitting data between devices, either wired or wireless mediums. It encompasses both synchronous and asynchronous communication modes, each offering distinct advantages and limitations. Understanding the transmission modes - simplex, half-duplex, and full-duplex - provides insight into the directionality of data flow between communicating devices. SPI communication, operating under full-duplex transmission and synchronized with a clock signal, enables simultaneous bidirectional data transfer between the master and slave devices, making it suitable for high-speed applications. While SPI offers advantages such as high-speed data transfer and simple implementation, it may face challenges like limited distance and increased wiring complexity in systems with multiple slave devices. On the other hand, I2C communication, with its simplicity and support for multi-master operation, caters to low-speed, short-distance communication needs, despite potential drawbacks like slower data transfer rates and susceptibility to clock stretching issues. Lastly, UART communication stands out for its simplicity and versatility, but it may not be optimal for high-speed applications due to limited data transfer rates. Overall, each serial communication protocol has its own pros and cons, but understanding them is necessary for selecting the best protocol for a given task.