Choosing between UART vs SPI for PLC modules is one of the most important decisions when designing smart lighting systems, industrial automation equipment, smart grids, and IoT networks. The selected interface directly affects communication speed, hardware complexity, power consumption, development costs, and overall system performance.
Among all available interfaces, UART (Universal Asynchronous Receiver/Transmitter) and SPI (Serial Peripheral Interface) are the two most commonly used options.
But which one should you choose? Before selecting an interface, engineers should understand the fundamentals explained in our article, What Is Power Line Communication (PLC)?
The answer depends on several factors, including transmission speed, hardware complexity, development cost, processing capability, and application requirements.
In this article, we’ll compare UART and SPI in detail and explain which interface is best suited for different PLC applications.
UART vs. SPI for PLC Modules: Which Interface Is Better?
As power line communication (PLC) technology becomes increasingly popular in smart lighting, industrial automation, smart grids, EV charging, and IoT applications, selecting the right communication interface between the host controller and the PLC module becomes critically important.
Among all available interfaces, UART (Universal Asynchronous Receiver/Transmitter) and SPI (Serial Peripheral Interface) are the two most commonly used options.
But which one should you choose?
The answer depends on several factors, including transmission speed, hardware complexity, development cost, processing capability, and application requirements.
In this article, we’ll compare UART and SPI in detail and explain which interface is best suited for different PLC applications.
UART vs SPI for PLC Modules: Understanding UART
UART is an asynchronous serial communication protocol that transfers data one bit at a time through dedicated transmission (TX) and reception (RX) lines. If you are a new user, can see our article How to Integrate a PLC Module into Embedded Systems.
Unlike synchronous interfaces, UART communication does not require a clock signal. Instead, both devices operate according to a predefined baud rate.
Typical UART connection
- TX (Transmit)
- RX (Receive)
- GND (Ground)
- Optional flow-control signals
Advantages of UART
- Simple hardware design
- Low implementation cost
- Fewer connection wires
- Excellent compatibility with microcontrollers
- Easy debugging and testing
Limitations of UART
- Lower transmission speed
- Higher communication latency
- Greater susceptibility to timing mismatches
- Limited scalability
UART vs SPI for PLC Modules: Understanding SPI
SPI is a synchronous communication protocol that uses a clock signal generated by the master device. This can see the IEEE standard for reference.
Because both devices share the same timing reference, SPI can achieve significantly higher transmission speeds than UART.
Typical SPI connection
- MOSI (Master Output Slave Input)
- MISO (Master Input Slave Output)
- SCLK (Clock)
- CS (Chip Select)
Advantages of SPI
- High-speed communication
- Lower latency
- Full-duplex operation
- Excellent performance in data-intensive applications
- More efficient data transfer
Limitations of SPI
- More complicated hardware design
- Additional wiring requirements
- Higher software development complexity
- Shorter communication distance
UART vs. SPI: A Detailed Comparison
| Feature | UART | SPI |
|---|---|---|
| Synchronization | Asynchronous | Synchronous |
| Clock signal | Not required | Required |
| Communication mode | Full duplex | Full duplex |
| Typical speed | 9.6 kbps–1 Mbps | Several Mbps to tens of Mbps |
| Wiring complexity | Low | Medium |
| CPU overhead | Moderate | Low |
| Implementation cost | Lower | Slightly higher |
| Scalability | Limited | Better |
| Debugging difficulty | Easy | Moderate |
| PLC module suitability | Entry-level systems | High-performance systems |
PLC Module vs PLC Chipset: Key Differences Explained this article may help you know more about it.
Why Many PLC Modules Support Both Interfaces
Modern PLC module manufacturers frequently provide both UART and SPI interfaces because different applications have different requirements.
UART is commonly selected for:
- Smart street lighting systems
- Building automation
- Environmental monitoring systems
- Remote metering
- Low-bandwidth sensor networks
SPI is often preferred for:
- Industrial automation systems
- AI vision lighting platforms
- Edge computing applications
- High-density sensor networks
- Real-time control systems
For example, a smart streetlight controller may only transmit switching commands, dimming instructions, and sensor data, making UART a cost-effective solution.
However, an industrial PLC gateway that processes large amounts of data from multiple nodes may require the higher throughput provided by SPI.
Key Factors to Consider When Selecting an Interface
1. Transmission speed
If your application requires rapid data exchange, SPI is usually the better choice.
2. Hardware resources
Small microcontrollers often have limited pins and memory resources, making UART more attractive.
3. Software complexity
UART drivers are generally easier to develop and maintain.
4. Electromagnetic interference (EMI)
Industrial environments often contain heavy electrical noise. Proper filtering, shielding, and isolation become essential regardless of the chosen interface.
5. Future scalability
Applications expected to support additional sensors, gateways, or edge computing capabilities may benefit from SPI’s higher bandwidth.
Typical PLC Module Architecture
A typical embedded PLC solution usually consists of the following components:
- Host microcontroller (MCU)
- UART or SPI interface
- PLC modem chip
- Analog front-end circuit
- Power coupling circuit
- Power line network
This architecture allows engineers to integrate PLC technology into smart lighting systems, industrial control equipment, and energy management platforms while minimizing development complexity.
UART vs SPI for PLC Modules: Which Interface Should You Choose?
The following recommendations can serve as a practical guideline:
| Scenario | Recommended interface |
|---|---|
| Low-cost devices | UART |
| Fast deployment | UART |
| Limited MCU resources | UART |
| High-speed communication | SPI |
| Real-time applications | SPI |
| Industrial automation | SPI |
| Large PLC networks | SPI |
Ultimately, neither interface is universally better. The right decision depends entirely on your system architecture and performance requirements.
