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Read the interface and driving method of the embedded LCD, and quickly collect it.
There are various types of LCD interfaces, and their classification is quite detailed. The main distinction is based on the driving mode and control method. On mobile devices, several common color LCD connection types include MCU mode, RGB mode, SPI mode, VSYNC mode, MDDI mode, and DSI mode. MCU mode is also sometimes referred to as MPU mode. Among these, only the TFT module supports an RGB interface.
However, in practical applications, MCU mode and RGB mode are more commonly used. Their differences are outlined below:
1. **MCU Interface**: This mode involves decoding commands, with a timing generator producing timing signals to drive the COM and SEG drivers.
2. **RGB Interface**: When it comes to setting up LCD registers, there's no difference between the MCU interface and the RGB interface. The key distinction lies in how the image data is written.
In MCU mode, the data can be stored in the internal GRAM of the IC before being sent to the screen. This allows the LCD to be directly connected to the memory bus. In contrast, the RGB mode lacks internal RAM. Instead, signals like HSYNC, VSYNC, ENABLE, CS, RESET, and RS are connected directly to the GPIO ports of the system, with waveforms generated using those ports.
Another key difference is that in MCU mode, display data is written to DDRAM, making it suitable for still images. In RGB mode, data is written directly to the screen, which is faster and ideal for video or animation.
The primary differences between MCU and RGB interfaces are:
- **MCU Mode**: Data is stored in DDRAM, suitable for static images.
- **RGB Mode**: Data is written directly to the screen, enabling faster updates for dynamic content.
**MCU Mode**
This mode is named after its use in microcontroller-based systems and is widely found in low-end and mid-range mobile phones due to its cost-effectiveness. It follows the Intel 8080 bus standard, often referred to as I80. There are two common variants: 8080 mode and 6800 mode, differing mainly in timing. The data width can range from 8-bit to 24-bit. Connections typically involve CS/, RS (register select), RD/, WR/, and the data lines. The advantage is simple control without needing clock or synchronization signals, but it requires GRAM, limiting the screen size to around 3.8 inches or smaller. The internal chip in an MCU-LCD module is called the LCD driver, which converts host data into pixel RGB values for display, without requiring point, line, or frame clocks.
**M6800 Mode**
This mode supports optional bus widths of 8/9/16/18 bits (default is 8 bits). Its design is similar to I80, but instead of separate read/write signals, it combines them with a latch signal (E). This makes it slightly different in implementation but functionally similar.
**I8080 Mode**
The I80 mode uses five control pins: CS (chip select), RS (register select), /WR (write enable), /RD (read enable), and RESET. It is simple to control and does not require clock or sync signals, but it consumes GRAM, making it unsuitable for large screens (QVGA or higher).
**VSYNC Mode**
This mode adds a VSYNC signal to the MCU interface, allowing for smoother animation updates. It synchronizes internal operations with external signals, enabling faster animation than traditional MCU modes. However, it has limitations in write speed, requiring the internal SRAM to be written faster than it is read.
**RGB Mode**
This mode is commonly used for larger screens, supporting data widths of 6, 16, 18, and 24 bits. Connections usually include VSYNC, HSYNC, DOTCLK, CS, RESET, and some may require RS. Unlike MCU mode, RGB mode does not use internal memory; instead, the system memory stores the image data, which is then transferred via DMA to the LCM. This results in faster display speeds, making it ideal for video and animations.
For RGB-LCD modules, the host outputs direct RGB pixel data, eliminating the need for conversion (except for gamma correction). A controller in the host generates RGB data along with point, line, and frame sync signals.
**TTL vs. LVDS Interfaces**
Color TFT LCDs primarily use TTL (RGB) or LVDS (differential signal) interfaces. TTL is common for small screens (up to 12.1 inches), while LVDS is used for larger screens (8 inches and above). TTL has many lines and short transmission distances, whereas LVDS offers longer distances with fewer lines. For large screens, control pins such as VSYNC, HSYNC, VDEN, and VCLK are used, with S3C2440 supporting up to 24 data lines (VD[23-0]).
The image data from the CPU or graphics card is usually a TTL signal (0–5V, 0–3.3V, etc.), which is transmitted at high speed. However, TTL signals have poor noise immunity over long distances, leading to alternatives like LVDS, TDMS, GVIF, P&D, DVI, and DFP. These formats encode the TTL signal for better transmission and decoding on the LCD side.
**Note**: TTL and LVDS are different signal transmission methods. TTL uses high/low levels to represent 1/0, while LVDS uses differential pairs to indicate logic states.
**SPI Mode**
This mode is less commonly used, involving 3 or 4 lines (CS/, CLK, SDI, SDO). While the connections are simple, the software control is more complex.
**MDDI Mode**
Developed by Qualcomm in 2004, MDDI improves reliability and reduces power consumption by minimizing connectivity. It replaces SPI and serves as a high-speed serial interface for mobile devices. Connections include host_data, host_strobe, client_data, client_strobe, power, and GND.
**DSI Mode**
DSI (Display Serial Interface) is a high-speed bidirectional command transmission mode, featuring differential pairs for data and clock signals (D0P, D0N, D1P, D1N, CLKP, CLKN). It is widely used in modern mobile devices for fast and efficient communication with the display.