Comparison of LCD Interface: RGB vs. SPI

Here is a quick summary of the core differences:

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.