A Complete Guide to PCB Interfaces and Communication Protocols

The choice of the PCB interface plays a critical role in enabling efficient protocol layering, minimizing crosstalk, and supporting advanced techniques like differential signaling and adaptive equalization.
As a PCB designer, understanding circuit board interfaces will help you choose and implement the right one. This ensures minimal signal loss, compatibility between components, and prevents system failures or board respins.

Highlights:

1. PCB interfaces are electrical and logical connections that enable data, power, and control signal transmission through protocols like SPI, I2C, Bluetooth, or Wi-Fi.
2. Circuit board interfaces are categorized into wired (e.g., UART, I2C, PCIe) and wireless (e.g., Bluetooth, Wi-Fi, LoRa).
3. The choice of interface depends on factors like data transfer speed, communication distance, system complexity, power consumption, and environmental conditions.

In this blog, you’ll learn about wired and wireless PCB interfaces and their roles in enabling communication between components. Each interface is briefly explained, followed by a table highlighting its key characteristics, such as communication type, speed, distance, typical applications, and pros and cons.

What are PCB interfaces?

Printed board interfaces are the electrical and logical connections that enable communication between the board and other components or devices. They define how data, power, or control signals are transmitted using specific protocols or standards, such as SPI, I2C, Bluetooth, or Wi-Fi.

An interface isn’t the same as a PCB connector. A connector is the physical part (like a port or plug) that connects the board to external devices. In contrast, an interface is the entire system that works over that physical link, including the signal lines and the protocols.

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What are the different types of circuit board interfaces?

PCB interfaces are categorized based on how they connect and communicate with other devices or components.

They can be broadly divided into two types:

1. Wired interfaces (like UART, I2C, or PCIe) use physical connections, such as cables or traces, to transmit data, power, or control signals.
2. Wireless interfaces (like Bluetooth, Wi-Fi, or LoRa) transmit data without physical connections, using radio waves or other wireless technologies. These are ideal for remote communication or applications where wiring is impractical.

The choice of the interface depends on the signal speed, distance, complexity, and power requirements.

19 wired PCB interfaces every designer should know

1. Universal asynchronous receiver/transmitter (UART)

UART is a simple asynchronous serial communication protocol that transmits data one bit at a time.

Unlike SPI or I2C, UART does not use a clock signal; instead, both devices must agree on a baud rate beforehand.

2. Serial peripheral interface (SPI)

SPI is a widely used interface for high-speed, full-duplex communication between microcontrollers and peripheral ICs like sensors, ADCs, DACs, shift registers, and SRAM. It allows simultaneous data transmission by both master and slave devices.

3. Inter-integrated circuit (I2C)

I2C is a two-wire serial communication protocol that allows multiple devices to share a single communication bus. It supports multiple controllers capable of transmitting and receiving data and commands.

Data is transferred in byte-sized packets, with each target device identified by a unique address.

4. Inter-IC sound (I2S)

I2S is a synchronous serial communication protocol designed specifically for transmitting digital audio data between integrated circuits.

Unlike UART, I2S uses a clock signal to synchronize data transmission and supports separate lines for audio data, word select, and bit clock, making it ideal for high-quality stereo audio streaming.

5. RS-232

RS-232 is a standard for serial communication using single-ended signaling, typically for point-to-point connections over short distances.

6. RS-485

It is a serial communication standard that uses differential signaling. RS-485 supports multiple devices on a bus over longer distances.

7. Universal serial bus (USB)

It is a standardized wired protocol used to connect peripherals to computers, supporting plug-and-play and data/power transfer over a four-wire interface.

8. Ethernet

Ethernet is a widely used networking protocol for wired local area networks (LANs), using twisted-pair cables to transmit data in frames based on the IEEE 802.3 standard.

9. FireWire (IEEE 1394)

FireWire is a high-speed, serial communication protocol developed by Apple and standardized as IEEE 1394. It supports isochronous and asynchronous data transfer and has been widely used in multimedia applications.

FireWire allows peer-to-peer communication, enabling devices to talk to each other without a host (unlike USB). It also supports hot-swapping and real-time data transfer.

10. Controller area network (CAN)

The CAN communication protocol is a multi-master serial system commonly used in automotive and industrial applications for real-time data exchange over a two-wire bus.

11. Low-voltage differential signaling (LVDS)

It is a high-speed, low-power signaling method that uses differential pairs to transmit data with low noise and electromagnetic interference, making it suitable for routing high-speed PCBs.

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12. Peripheral component interconnect express (PCIe)

PCIe is a high-speed serial expansion bus standard that connects internal components like GPUs and SSDs to a motherboard.

13. High-definition multimedia interface (HDMI)

This is a popular digital interface for transmitting uncompressed video and audio data between devices like monitors and media players over a single cable.

14. Serial advanced technology attachment (SATA)

It is a computer bus interface for connecting mass storage devices like hard drives and SSDs using serial signaling for fast data transfer.

15. Secure digital input output (SDIO)

This wired interface type is an extension of the SD card standard that allows peripheral devices to interface with a host via the SD card slot using serial communication.

16. Mobile industry processor interface (MIPI)

MIPI defines low-power, high-speed serial interfaces, such as camera serial interface (CSI) and display serial interface (DSI). It is used for connecting cameras and displays to processors in mobile and embedded systems using differential data lanes.

17. Pulse width modulation (PWM)

This is a method of transmitting analog signal levels by varying the duty cycle of a digital signal, commonly used for motor control and dimming LEDs.

18. Double data rate (DDR)

DDR memory is a high-speed synchronous interface used to connect dynamic random-access memory (DRAM) to a memory controller, commonly found in processors, system on a chip (SoC), and field-programmable gate arrays (FPGAs). It transfers data on both the rising and falling edges of the clock signal, effectively doubling the data rate compared to single data rate (SDR) memory.

DDR operates with strict timing and signal integrity requirements, and its interface includes multiple signal types for command, address, control, and high-speed data transfer.

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19. Embedded multimedia card (eMMC)

eMMC is a non-volatile storage interface based on the multimedia card (MMC) standard, commonly used in smartphones, tablets, and embedded systems. It combines a flash memory device and a controller in a single BGA package, simplifying storage integration in hardware designs.

Unlike removable SD cards, eMMC is soldered directly onto the PCB and provides a managed NAND flash interface with wear leveling, bad block management, and error correction handled internally.

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9 types of wireless PCB interfaces

1. Wireless fidelity (Wi-Fi)

This is a wireless networking protocol based on IEEE 802.11 standards, enabling devices to connect to local area networks and the internet using radio waves.

To learn how to design RF boards, see RF PCB design: 9 factors to consider.

2. Bluetooth

A Bluetooth interface enables wireless communication by forming a short-range network called a piconet, which includes one master device and multiple slave devices that communicate directly with the master.

Several interconnected piconets can form a larger structure known as a scatternet, where certain devices, called bridge nodes, participate in more than one piconet to facilitate communication between them.

Sierra Circuits manufactures high-precision RF and microwave PCBs with tightly controlled impedance and low signal loss. See RF and microwave PCB capabilities to learn more.

3. ZigBee (802.15.4)

In ZigBee communication, devices form a mesh network where data is transmitted between nodes using short-range, low-power wireless signals. The network includes the following devices and nodes.

• Coordinator- Central device that initiates, manages, and secures the network. Only one exists per network.
• Routers (nodes) – Forward data between devices, extending network range.
• End devices- Send and receive data via a parent router.

Messages can hop through multiple nodes to reach their destination, enabling reliable communication even over longer distances or around obstacles.

4. Long range (LoRa)

As the name suggests, LoRa is a long-range, low-power, wireless communication protocol used for IoT networks, especially where wide coverage and low data rates are needed.

LoRa end nodes use sensors to collect data and wirelessly transmit it to nearby LoRaWAN gateways, which forward it to the cloud. Multiple gateways within range can receive the same signal, forming a star-on-star topology that enhances network reliability and coverage.

5. Near field communication (NFC)

NFC is a short-range wireless communication protocol enabling data exchange over distances of a few centimeters, commonly used for contactless payments.

6. 5th generation (5G)

This fifth-generation cellular network standard offers ultra-fast data rates, low latency, and massive device connectivity for mobile and IoT applications.

To learn more about designing 5G boards, see how to design PCBs for 5G wireless applications.

7. Satellite communication

This wireless technology enables long-distance communication using satellites to transmit and receive signals between ground stations and devices globally.

The IEEE categorizes satellite communication frequencies into the C, X, Ku, and Ka bands, as outlined below.

The exact frequency ranges can vary by region and application, and are often classified to prevent interference or ensure security.

8. Radio frequency identification (RFID)

It is a wireless identification system that uses electromagnetic fields to read and write data from tags attached to objects, often used in tracking and access control.

9. Z-Wave

Z-Wave is a low-power, wireless communication protocol designed for smart home and automation systems, commonly integrated into PCBs to enable device connectivity. It operates on a mesh network topology, allowing devices to relay messages to extend range and reliability.

Unlike UART, Z-Wave is not a hardware-level interface but a wireless protocol layer that typically runs on a SoC or module, which communicates with a host microcontroller via serial interfaces like UART or SPI.

Key takeaways:

1. A PCB interface defines the methods for data exchange over physical connections.
2. Connectors are the physical hardware links, while printed circuit board interfaces define the communication protocols that operate over those connections.
3. Common wired interfaces include UART, SPI, I2C, I2S, RS-232, RS-485, USB, Ethernet, FireWire, CAN, LVDS, and PCIe.
4. Key wireless interfaces comprise Bluetooth, Wi-Fi, LoRa, ZigBee, and NFC, used for cable-free communication between devices.
5. Each interface has unique properties: data lines, communication mode, speed, distance, applications, advantages, and disadvantages.
6. Understanding interface specifics helps PCB designers optimize board layout, enhance signal integrity, ensure electrical and protocol compatibility between components, and improve overall system reliability.

Understanding PCB interfaces is essential for designing robust electronic systems. By selecting and implementing appropriate interfaces, electrical engineers can ensure low-loss communication between components in modern devices.

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