Serial communication remains one of the most widely used methods for connecting embedded devices, even in modern systems that include high-speed networking and multimedia interfaces. In single board computers (SBCs), serial ports continue to play an essential role in system debugging, industrial communication, and device integration. Engineers working with embedded platforms often rely on serial interfaces to connect sensors, controllers, and legacy industrial equipment.
This article provides a practical introduction to serial communication on SBC platforms. It explains how serial ports work, the role of UART controllers, the differences between common serial standards, and how these interfaces are typically used in embedded Linux systems.
Introduction to Serial Communication
In digital communication, two basic methods are commonly used to transmit data between devices: parallel communication and serial communication. Parallel interfaces send multiple bits simultaneously through several wires, while serial communication sends data sequentially, one bit at a time, through a single channel.
Although parallel communication can theoretically transmit data faster, serial communication offers several advantages that make it ideal for embedded systems. It requires fewer wires, simplifies circuit design, and provides stable communication across longer distances.
A typical serial connection uses two primary signals:
TX (transmit) – the line used to send data
RX (receive) – the line used to receive data
Most systems also include a shared ground reference to complete the circuit. Some implementations add additional control signals such as RTS and CTS for flow control.
Because the hardware requirements are minimal, serial interfaces are commonly used in microcontrollers, industrial controllers, and SBC platforms.
Why Serial Ports Are Still Used in Modern SBCs
Despite the rise of interfaces such as USB, PCIe, and Ethernet, serial communication remains essential in embedded computing environments.
One reason is its simplicity. A serial interface can be implemented using only a few pins on the processor, which makes it easy to integrate into system designs.
Another advantage is reliability. Serial communication protocols have been used for decades and are extremely well understood. They are less sensitive to timing issues compared with complex high-speed interfaces.
Serial ports are also crucial during system development. Many SBC platforms expose a debug UART port that allows developers to monitor the boot process and access the system console.
In addition, many industrial devices still rely on serial communication standards. SBCs used in automation systems often need to communicate with equipment that uses RS232 or RS485 interfaces.
Understanding UART in Embedded Systems
At the hardware level, most SBC serial communication is implemented through UART controllers. UART stands for Universal Asynchronous Receiver Transmitter.
A UART module converts parallel data from the processor into serial data for transmission through the communication line. When data is received, the UART converts the incoming serial data back into parallel form so the CPU can process it.
UART communication is asynchronous, meaning it does not require a separate clock signal. Instead, both devices must be configured with the same communication parameters so they can interpret the data correctly.
These parameters include:
baud rate
number of data bits
parity setting
number of stop bits
If both devices use identical settings, they can exchange data successfully over the serial link.
Key UART Communication Settings
Before establishing a UART connection, both communicating devices must use identical serial settings.
Baud Rate
The baud rate determines how quickly data is transmitted. It represents the number of signal changes per second.
Common baud rates include:
9600
38400
115200
In many embedded Linux systems, the default console speed is 115200 baud.
Data Bits
The data bit setting defines how many bits represent a single character. Most modern systems use 8 data bits.
Parity
Parity provides a simple error detection mechanism. It can be configured as even, odd, or disabled.
Many embedded devices operate without parity to simplify communication.
Stop Bits
Stop bits indicate the end of each data frame. Most UART systems use one stop bit.
A common serial configuration often written as “115200 8N1” means:
115200 baud
8 data bits
no parity
1 stop bit
Common Serial Interface Standards
Several serial communication standards are used in SBC systems depending on the application environment.
TTL UART
TTL-level UART is the most basic form of serial communication used inside embedded devices. The signal voltage usually corresponds to the processor’s logic level, typically 3.3 volts.
TTL UART connections are frequently used for:
debug consoles
communication with microcontrollers
GPS modules
sensor interfaces
Because the voltage levels are relatively low, TTL UART connections are generally used over short distances.
RS232
RS232 is one of the oldest serial communication standards still in use today. It uses higher voltage levels than TTL UART and can transmit data over longer cables.
Typical RS232 signals range between positive and negative voltages, often around ±12 volts. Because SBC processors operate at much lower voltages, a level conversion chip is required to interface between UART and RS232 signals.
RS232 is still used in many applications such as industrial machinery, laboratory equipment, and legacy control systems.
RS485
RS485 is widely used in industrial automation networks. Unlike RS232, which uses single-ended signaling, RS485 uses differential signaling.
Differential signaling improves noise immunity and allows communication over long distances, sometimes up to 1200 meters.
Another advantage of RS485 is its ability to support multiple devices on a single communication bus. This makes it ideal for industrial networks that connect multiple sensors and controllers.
Many industrial protocols, including Modbus RTU, rely on RS485 communication.
Serial Interfaces in Linux-Based SBC Platforms
Most modern SBC platforms run Linux-based operating systems. In Linux, serial ports are represented as device files within the /dev directory.
Examples include:
/dev/ttyS0
/dev/ttyS1
/dev/ttyUSB0
Each device file corresponds to a specific UART controller or serial adapter.
Developers can access these devices using terminal software such as minicom, screen, or picocom. These tools allow engineers to interact with serial devices and monitor data transmission.
Serial Console for System Debugging
The serial console is one of the most important debugging tools for embedded developers.
During the boot process, the bootloader and Linux kernel typically output diagnostic messages through a serial port. By connecting a serial terminal, developers can monitor the system startup sequence and detect errors.
The serial console can also provide access to a command-line shell, allowing engineers to control the system even if the graphical interface fails to start.
Because of this reliability, most SBC development boards expose a dedicated debug UART header.
Typical Applications of SBC Serial Ports
Serial communication is used in many types of embedded systems.
Industrial Automation
Industrial control systems frequently use RS485 interfaces to connect programmable logic controllers, sensors, and monitoring equipment.
IoT Devices
Many IoT modules communicate with SBC platforms through UART connections. These may include wireless communication modules, GPS receivers, or environmental sensors.
Device Debugging
Engineers rely heavily on serial ports during the development and testing phases of embedded systems.
Microcontroller Communication
In some designs, the SBC serves as the main processor while smaller microcontrollers handle low-level hardware control. Serial communication allows the two systems to exchange commands and status information.
Hardware Design Considerations
When designing an SBC system that includes serial interfaces, several hardware factors must be considered.
Voltage Compatibility
The voltage levels of connected devices must match. Connecting incompatible voltage signals may damage hardware components.
Signal Quality
Long communication cables can introduce noise and signal degradation. Differential communication standards such as RS485 are often used in industrial environments to improve reliability.
Electrical Protection
Industrial designs often include protection components such as ESD protection circuits or surge suppressors to protect the system from electrical disturbances.
Conclusion
Serial communication continues to play a vital role in embedded computing systems. Even as new high-speed interfaces emerge, serial ports remain indispensable for debugging, device communication, and industrial system integration.
By understanding UART communication principles and the differences between serial standards such as TTL, RS232, and RS485, engineers can design reliable communication interfaces for SBC platforms.
From development debugging to industrial automation, serial communication remains one of the most practical and widely used technologies in embedded system design.
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