Introduction There are many kinds of LCD interfaces, with wide range of applications. The classification criteria mainly depends on the driving mode and control mode of the LCD. At present, there are generally several connection modes for color LCDs on mobile phones: MCU mode, RGB mode, SPI mode, VSYNC mode, MDDI mode, DSI mode, etc. and only the TFT module has RGB interface. Basics of LCD Interfacing Catalog Introduction Ⅰ LCD Interface Modes 1.1 MCU Mode 1.2 VSYNC Mode 1.3 M6800 Mode 1.4 Intel 8080 Mode 1.5 RGB Mode 1.6 SPI (Serial Peripheral Interface) Mode 1.7 MDDI (Mobile Display Digital Interface) Mode 1.8 DSI (Display Serial Interface) Mode Ⅱ MCU Mode vs RGB Mode Ⅲ TFT-LCD Interface Explained 3.1 TTL Interface 3.2 LVDS 3.3 EDP (Embedded Display Port) 3.4 MIPI Interface Ⅳ FAQ Ⅰ LCD Interface Modes The following is a detailed explanation of the different interface modes: 1.1 MCU Mode It is mainly used in the field of single-chip microcomputers. Later, it is widely used in low-end mobile phones, and its main feature is that it is cheap. The standard term for the MCU-LCD interface is the 8080 bus standard proposed by Intel. Figure 1. Intel 8080 Therefore, 8080 is used to refer to the MCU-LCD screen in many documents. It can be mainly divided into 8080 mode and 6800 mode, and the difference between the two is mainly the timing. There are 8 bits, 9 bits, 16 bits, 18 bits, and 24 bits for data bit transfer. Connections are divided into: CS/, RS (register selection), RD/, WR/, and data lines. The advantages are: the control is simple and convenient, no clock and synchronization signals are required. The disadvantage is: it consumes GRAM, so it is difficult to achieve a large screen (above 3.8). For LCM with MCU interface, the internal chip is called LCD driver. The main function is to transform the data/command sent by the host into the RGB data of each pixel, so that it can be displayed on the screen. This process does not require point, line, frame clocks.The LCD Driver IC of the MCU interface is equipped with GRAM. As a co-processor of the MCU, it accepts the Command/Data sent by the MCU and can work relatively independently. Pay attention to, the internal chip of LCD Module (LCM) is called the LCD driver. The main function is to transform the data/commands sent by the host computer into the RGB data of each pixel, so that it can be displayed on the screen. This process also does not require point, line, frame clocks. 1.2 VSYNC Mode In fact, this mode is to add a VSYNC signal to the MCU mode and applied to the update of the moving picture, which is very different from the above interface. This mode supports the function of direct animation display. It provides a solution for animation display with minimal changes to the MCU interface. In this mode, the internal display operation is synchronized with the external VSYNC signal. Animation display at a higher rate than internal operations can be achieved. However, due to the difference in its operation mode, this mode has a limit on the speed, that is, the write speed to the internal SRAM must be greater than the speed of the display read internal SRAM. 1.3 M6800 Mode The M6800 mode supports selectable bus widths of 8/9/16/18-bit (the default is 8 bits). The actual design idea is the same as that of Intel 8080. The main difference is the bus control read and write signals in this mode. Combined on one pin (with a latch signal (E) data bit transmission has 8, 9, 16 and 18 bits). Figure 2. M6800 Mode 1.4 Intel 8080 Mode Intel 8080 LCD interface is divided into: CS/, RS (register selection), RD/, WR/, and the data line. Advantage: Simple and convenient control, no clock and synchronization signals are required. Disadvantage: It consumes GRAM, so it is difficult to achieve a large screen (above QVGA). Figure 3. Intel 8080 Mode 1.5 RGB Mode The large screen adopts more modes, and the data bit transmission also has the 6-, 16- and 18-, 24-bit. The connections are generally: VSYNC, HSYNC, DOTCLK, CS, RESET, some also need RS, and the rest is the data line. Its advantages and disadvantages are just the opposite of MCU mode. The main difference between the MCU-LCD screen and the RGB-LCD screen is the location of the video memory. The video memory of RGB-LCD is acted by system memory, so its size is only limited by the size of system memory. Where RGB-LCD can be made larger, such as 4.3" can only be regarded as entry-level, and 7" in MID, 10" screens have begun to be widely used. At the beginning of the design of MCU-LCD, it was only necessary to consider that the memory of the single-chip microcomputer was small, so the video memory was built into the LCD module, and then the software updated the video memory through special display commands with small MCU screen. At the same time, the display update speed is slower than RGB-LCD. The display data transmission mode is also different. RGB screen only needs to organize the data in the video memory. After starting the display, the LCD-DMA will automatically transfer the data in the video memory through the RGB interface to the LCM, while the MCU screen needs to send a drawing command to modify the internal RAM of the MCU (that is, the RAM of the MCU screen cannot be directly written).Therefore, the RGB display speed is significantly faster than that of the MCU, and the MCU-LCD is also slower in terms of video playback. For the LCM of the RGB interface, the host directly outputs the RGB data of each pixel without conversion (except for GAMMA correction, etc.). For this interface, an LCD controller is required in the host part to generate RGB data and sync signals. Figure 4. RGB Mode Here gives a note. The color TFT LCD screen mainly has 2 kinds of interfaces: TTL interface (RGB color interface), and LVDS interface (differential signal transmission). The TTL interface is mainly used for small-sized TFT screens below 12.1 inches, and the LVDS interface is mainly used for large-sized TFT screens above 8 inches. The TTL interface has many lines and the transmission distance is short, while the LVDS interface has a long transmission distance and a small number of lines. The large screen adopts more modes, the control pins are VSYNC, HSYNC, VDEN, VCLK, S3C2440 supports up to 24 data pins, and the data pin is VD[23-0].The image data sent by the CPU or graphics card is a TTL signal (0-5V, 0-3.3V, 0-2.5V, or 0-1.8V), and the LCD itself also receives a TTL signal, which is transmitted at a high rate over long distances. However, its performance is poor, and the anti-interference ability is relatively poor. With the time goes by, a variety of transmission modes were proposed, such as LVDS, TDMS, GVIF, P&D, DVI and DFP. They actually just encode the TTL signal sent by the CPU or graphics card into various signals for transmission, and decode the received signal on the LCD side to obtain the TTL signal. No matter what transmission mode is used, the essential TTL signal is the same. Note: TTL/LVDS are two signal transmission modes: TTL is a mode in which high level means 1, and low level means 0; LVDS is the difference of a positive and negative corresponding waveform used to indicate the 1 or 0. 1.6 SPI (Serial Peripheral Interface) Mode It is less used. There are 3-wire and 4-wire, the connection is CS/, SLK, SDI, and SDO, and the software control is more complicated. 1.7 MDDI (Mobile Display Digital Interface) Mode Qualcomm's MDDI, which can improve the reliability of mobile phones and reduce power consumption by reducing wiring. It will replace SPI mode as a high-speed serial interface in the mobile field. The main connection is host_data, host_strobe, client_data, client_strobe, power, and GND. 1.8 DSI (Display Serial Interface) Mode This mode is a serial bidirectional high-speed command transmission mode, with D0P, D0N, D1P, D1N, CLKP, CLKN connected. Ⅱ MCU Mode vs RGB Mode Among them, there are more applications in MCU mode and RGB mode. The differences are as follows:1) MCU interface: it will decode commands, generate timing signals by timing generator, and drive COM and SEG.RGB interface: When writing LCD register setting, it is no different from MCU interface. The difference is only in how the image is written.2) When using the MCU mode, since the data can be stored in the IC's internal GRAM first and then written to the screen, the LCD in this mode can be directly connected to the memory bus. It is different when using RGB mode, and has no internal RAM, HSYNC, VSYNC, ENABLE, CS, RESET, RS can be directly connected to the GPIO port of memory, and use the GPIO port to simulate waveforms.3) MCU Interface vs RGB InterfaceThe main differences between the MCU interface and the RGB interface are:MCU interface mode: display data is written into DDRAM, often used for still picture display.RGB interface mode: The display data is not written into DDRAM, but directly written to the screen, which is fast and often used to display video or animation. Ⅲ TFT-LCD Interface Explained The commonly used interfaces of TFT-LCD, including TTL (RGB), LVDS, EDP, and MIPI. Here roughly talk about the basic principles of the signal composition of these interfaces. Figure 5. TTL (Transistor-Transistor Logic) Schematic 3.1 TTL Interface 🔺Interface OverviewTTL is transistor-transistor logic, and TTL level signals are generated by TTL devices. TTL devices are a large category of digital integrated circuits. They are manufactured by bipolar technology and have the characteristics of high speed, low power consumption and many varieties.The TTL interface is an interface for transmitting data in parallel. When using it, it is not necessary to use a dedicated interface circuit at the driver board end and the LCD panel end of the liquid crystal display, but the TTL data signal output by the main control chip of the driver board is transmitted through the cable. It is directly transmitted to the input interface of the LCD panel. Due to the high signal voltage, many connections and long transmission cables of the TTL interface, the anti-interference ability of the circuit is relatively poor, and it is easy to generate electromagnetic interference (EMI). In practical applications, TTL interface circuits are mostly used to drive small-size (below 15in) or low-resolution LCD panels. The highest pixel clock of TTL is only 28MHz.TTL is the only signal that TFT-LCD can recognize. Early digital processing chips are all TTL, that is, RGB is directly output to TFT-LCD.🔺Signal TypesThe TTL output interface of the driver board generally includes three types of signals: RGB data signal, clock signal and control signal. As shown below:(1) RGB Data-Signala. Single Channel6-BitAs for it, there are 18 RGB data lines in total, including 6 R0~R5 red primary color data lines, 6 G0~G5 green primary color data lines, 6 B0~B5 blue primary color data lines, a total of 18 strips. Since the primary color RGB data is 18bit, it is also called 18-bitTTL interface.8-BitFor it, there are a total of 24 RGB data lines, including 8 R0~R7 red primary color data lines, 8 B0~B7 green primary color data lines, 8 BO~B7 blue primary color data lines, a total of 24 strips. Since the primary color RGB data is 24-bit, it is also called 24-bit TTL interface.b. Dual ChannelDual channels, that is, two sets of RGB data, which are divided into odd channels and even channels. Some clocks are also divided into OCLK/ECLK, and some share one. The following figure has two, as shown below:6-BitIt has 36 RGB data lines in total, including 18 odd RGB data lines, 18 even RGB data lines. Since the primary color ROB data is 36-bit, it is also called 36-bitTTL interface.8-BitIt has 48 RGB data lines, including 24 odd RGB data lines and 24 even RGB data lines. Since the primary color RGB data is 48bit, it is also called 48-bit TTL interface.(2) Clock SignalIt refers to the pixel clock signal, which is the benchmark for transmitting data and reading the data signal. When using odd/even pixel dual way to transmit RGB data, different output interfaces use different methods of pixel clock. Some output interface odd/even pixel dual data share a pixel clock signal, and the others set odd pixel data clock and even pixel two clock signals to meet the needs of different LCD panels.(3) Control SignalThe control signals include a data enable signal (or an effective display data strobe signal) DE, a horizontal sync signal HS, and a vertical sync signal VS. 3.2 LVDS 🔺Overview of LVDS InterfaceLVDS is a low-voltage differential signaling technology interface. A digital video signal transmission method developed to overcome the shortcomings of large power consumption and large EMI electromagnetic interference when transmitting broadband high bit rate data in TTL level mode. The LVDS output interface uses a very low voltage swing (about 350mV) to transmit data differentially on two PCB traces or a pair of balanced cables, that is, low-voltage differential signaling. Using the LVDS output interface, the signal can be transmitted at a rate of several hundred Mbit/s on the differential PCB line or balanced cable. Due to the low-voltage and low-current driving method, low noise and low power consumption are achieved.🔺Composition of LVDS Interface CircuitIn a liquid crystal display, the LVDS interface circuit includes two parts, the LVDS output interface circuit (LVDS transmitter) on the motherboard side and the LVDS input interface circuit (LVDS receiver) on the LCD panel side. The LVDS emitter converts the TTL signal into an LVDS signal, and then transmits the signal to the LVDS decoding IC on the receiving end through the flexible cable (line) between the driver board and the LCD panel, and the LVDS receiver then serializes the serial signal which is converted into a parallel signal of TTL level, and sent to the LCD screen timing control and row and column drive circuit. In other words, TFT only recognizes TTL (RGB) signals.🔺Signal type of LVDS interfaceLVDS signals are composed of data differential and clock differential signals. As shown below:(1) Single Channel6-Bit DataThere are 4 sets of differential lines, 3 sets of signal lines, and one set of clock lines, including Y0M, Y0P, Y1M, Y1P, Y2M, Y2P, CLKOUT_M, CLKOUT_P.8-Bit DataThere are 5 groups of differential lines, 4 groups of signal lines, and a group of clock lines. They are Y0M, Y0P, Y1M, Y1P, Y2M, Y2P, CLKOUT_M, CLKOUT_P.(2) Dual ChannelWhen LVDS transmits data with higher resolution, the anti-interference ability is relatively strong. But when the resolution is higher than 1920×1080, the single channel is overwhelmed, so there is a dual interface. Its purpose is very simple, speed up and enhance anti-interference ability.6-Bit DataIt is exactly twice as long as the single channel, and the clock is also two channels. The red part: the two sets of signals: Y3M, Y3P, Y3M1, and Y3M1 are not connected.8-Bit DataSimilar to the previous comparison. 3.3 EDP (Embedded Display Port) EDP is a communication interface of the computer display screen. The resolution of the computer using the EDP display interface will be higher than that of the LVDS interface. Generally, high-definition screens use this communication interface. It is a fully digital interface based on the DisplayPort architecture and protocol. It can transmit high-resolution signals with simpler connectors and fewer pins, and can achieve simultaneous transmission of multiple data, so the transmission rate is much higher than LVDS. 3.4 MIPI Interface Compared with the LVDS interface, the MIPI interface is rare, but in fact, it has many advantages. The MIPI interface module has the advantages of high speed, large amount of data transmission, low power consumption, and good anti-interference when compared with the parallel port. It is more and more favored by customers and is growing rapidly. For example, an 8M module with both MIPI and parallel port transmission requires at least 11 transmission lines and an output clock of up to 96M to achieve a full pixel output of 12FPS when using an 8-bit parallel port. Channel 6 transmission lines can achieve a frame rate of 12FPS at full pixels, and the current consumption will be about 20MA lower than that of parallel port transmission. Since MIPI uses differential signal transmission, the design needs to be strictly designed according to the general rules of differential design. The key is to achieve differential impedance matching. The MIPI protocol stipulates that the differential impedance of the transmission line is 80-125 ohms. Ⅳ FAQ 1. What is LCD interface?16x2 LCD means that there are two rows in which 16 characters can be displayed per line, and each character takes 5X7 matrix space on LCD. ... In this tutorial we are going to connect 16X2 LCD module to the 8051 microcontroller (AT89S52). 2. What is LCD parallel interface?LCD Displays that use a parallel interface include Character, Graphic and TFT. ... The initial step is to energize the LCD. Reads and Writes are sent via 8 data lines and 3 control lines. These control lines are Read/Write (R/W), Enable (E) and Register Select (RS). 3. What is TFT interface?A TFT LCD display module consists of a TFT LCD panel, one or more COG (chip-on-glass) or COB (chip-on-board) driver ICs, a backlight, and an interface. Several TFT display interface technologies exist today. Picking the right interface depends on specific end-product concerns. 4. What are the different types of LCDs?Different Types of LCD PanelsTwisted Nematic (TN) Twisted Nematic LCDs are the most commonly manufactured and used types of monitors across a wide range of industries. ...IPS Panel TechnologyVA PanelAdvanced Fringe Field Switching 5. What is MCU interface?The MCU interface has two standard types, the Intel-8080 and Motorolla-6800 series. These interfaces communicate through read, write and chip-select signals to address registers or display RAM. The slight difference between the two pertains to the direction and separation of the write and read signals. 6. What is MCU interface LCD?These interfaces communicate through read, write and chip-select signals to address registers or display RAM. Depending on color depth (8, 9, 16 or 18-bit), MCU sends RGB signals directly to LCM's display memory. 7. Is TFT an LCD?TFT is a kind of LCD. The TFT(Thin Film Field-effect Transistor) is a video in which every single pixel in the liquid crystal display is actuated by a Thin Film Transistor embedded in the rear. Thus can achieve high speed, high brightness, high contrast display screen information.
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