Aug 27, 2025
Here is a quick summary of the core differences:
Feature
RGB Interface
SPI Interface
Type
Parallel Interface
Serial Interface
Working Principle
Directly streams pixel clock, sync signals, and parallel data (R, G, B channels).
Sends pixel data byte-by-byte using clock (SCK), data out (SDA/MOSI), and chip select (CS) lines.
Speed
Very High
Low
Typical Resolution
Medium to Large (QVGA, VGA, WVGA and higher)
Very Small (typically up to 240x320 pixels)
Pin Count
High (can be 20+ pins)
Very Low (typically 3-6 pins)
MCU Load
Low (Dedicated LCD controller or FSMC required)
High (CPU must manage and clock out all data)
Cost
Higher (for PCB and connector)
Lower
RGB Interface
Overview:The RGB (Red, Green, Blue) interface, often called a "Parallel" or "MCU" interface in its smart form, is a high-speed parallel interface. It uses separate data lines for each color component and synchronizing signals (HSYNC, VSYNC, DOTCLK) to push pixel data directly to the display.
Advantages:
High Speed & Performance: Ideal for smooth video, animations, and complex GUIs on larger screens due to its parallel nature.
Low CPU Overhead: The host MCU/MPU writes frame data to the display's memory once, or uses a dedicated controller, freeing the CPU for other tasks.
Real-time Display: Pixels are updated continuously without frame buffer manipulation delays from the host.
Disadvantages:
High Pin Count: Requires many GPIO pins on the host, making it complex and expensive for simple projects.
Complex PCB Design: Routing numerous high-speed parallel lines requires careful PCB layout to avoid signal integrity issues.
Higher Cost: More pins lead to more expensive connectors, cabling, and more complex MCUs/MPUs.
SPI Interface
Overview:The Serial Peripheral Interface (SPI) is a simple, low-pin-count serial communication protocol. It transmits display commands and pixel data one bit at a time over a single data line (or two for dual-SPI/quad-SPI for higher speed).
Advantages:
Very Low Pin Count: Typically requires only 3-4 pins (CS, SCK, SDA/MOSI), making it perfect for low-pin-count MCUs.
Simple Implementation: Easy to wire and program, with widespread library support on all platforms.
Low Cost: Simplifies PCB design and reduces component and connector costs.
Disadvantages:
Low Bandwidth: The serial nature is a major bottleneck for refreshing large amounts of pixel data, resulting in slow update rates.
High CPU Overhead: The CPU must actively clock out every byte of data for the screen, which can consume significant processing power.
Limited Practical Resolution: Generally only suitable for small displays (e.g., 128x160, 240x240) or for updating small portions of a screen.
How to Choose
The choice between RGB and SPI is a direct trade-off between performance and simplicity/cost.
Choose RGB for: Medium to large TFT displays, touchscreen GUIs, applications requiring smooth animations, video playback, or when the host CPU needs to be offloaded from the display refresh task.
Choose SPI for: Small OLED or TFT displays, simple status indicators, projects with limited MCU pins, low-cost applications, or when only simple graphics or text are needed.
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