What is the Display Interface?
For display purposes, the display controller provides an interface between the multimedia processor and a display module.
In the underlying logic, the display interface is the media to transfer the signals of the master controller to the display module.
In the TFT display module, the interface usually comes along in the FPC or PCB, and even in the extension of LCD controller boards.
6 Most Common Types of TFT Display Interfaces
In choosing the right TFT-LCD module for the development of terminals, the interface is one of the key factors you will consider. It relates to the display size, resolution, power, performance, and signal mapping between the devices.
There are many interface options available.
According to the driving and control mode of TFT-LCD, the main signal input interface types are as follows: MCU (also known as MPU), SPI, TTL (also known as RGB), LVDS, DSI (also known as MIPI), and EDP.
Comparison among all 6 interfaces
To make it easier for you, we have recapped their differences in utility, pros, and cons in following table.
For more details, you can find the explanation of the features and definition of each interface in the following contents:
MCU (Micro Control Unit)
The MCU interface is essential because it can write and read data stored in the internal frame buffer or the gadget’s storage.
This interface is mainly used for small-sized screens of under 5.0-inch, and a resolution of under 480*RGB*800.
Every MCU interface includes four types of signals:
- RD (Read enable signal in 8080 MCU interface)
- WR (Write enable signal in 8080 MCU interface)
- RS (Reset pin)
- CS (Chip select pin)
Data signals: 18-bit, 16-bit, 9-bit, or 8-bit
Multi-interface compatible can be selected by IM pin:
Interface definition example of MCU:
SPI（Serial Peripheral Interface）
SPI is a serial peripheral device interface.
It performs synchronous serial data transmission between the CPU and the Driver IC.
The data is transmitted in bits, with high bits in the front and low bits in the back.
It is full-duplex communication, and the transmission speed is only a few Mbps, which is slow.
Consequently, the serial port is usually used for low-resolution (below 320*480) screens and requires very few PINs.
At present, SPI displays are applied in many small applications. Such as smart wearables, and small home appliances.
The interface is mainly divided into two types: 3-line and 4-line
- SDA (DATA in/output pin)
- SCL (Serial interface clock)
- CS (Chip selection pin)
Multi-interface compatible can be selected by IM pin:
Interface definition example of SPI:
TTL-RGB (Transistor Transistor Logic-Red Green and Blue)
The TTL interface is a transistor-transistor logic interface.
The TTL level signal is generated by the TTL device.
The TTL interface transmits data in parallel. It superimposes the changes of the three color channels of red (R), green (G), and blue (B) and outputs them together.
The RGB data signal output by the master control chip is directly transmitted to the input interface of the LCD panel. Thus, it is also called the RGB interface.
The display data is not written to DDRAM, but directly to the screen. This interface is widely used in small and medium-sized sized-display. It is fast and often used to display video or animation.
Every RGB interface includes five types of signals:
- VS (Vertical Synchronization that synchronizes data for columns of pixels on display)
- HS (Horizontal Synchronization that synchronizes data for rows of pixels on display)
- D0…DXX (includes a separate line for each bit of information)
- DCLK (Dot Clock for synchronizing data)
- DE (Data Enable for confirming data transfer accuracy)
In terms of RGB mode, there is DE mode, SYNC mode, and SYNC-DE MODE.
For example, ST7282 RGB MODE:
In terms of the data bits, the RGB interface can be divided into 6-bit, 8-bit, 16-bit, 18-bit, and 24-bit, of which 6 and 8-bit are RGB serial ports.
Interface definition example of RGB24-bit:
MIPI-DSI (Mobile Industry Processor Interface – Display Serial Interface)
DSI is a display serial interface, which is a standard display interface defined by the MIPI Alliance (Mobile Industry Processor Interface Alliance).
Its advantages are lower power consumption, higher data transmission rate (about 1Gbps), and smaller layout space. In addition, it can transmit video data and control commands.
Hence, the interface mainly applies to terminals that require high-resolution displays, such as tablets, smartphones, and laptops.
In terms of the level of resolution, it can be divided into 1, 2, 3, 4, and 8 lanes.
Interface definition example of MIPI-DSI:
The table above shows MIPI 4-lane, in addition to 4 sets of MIPI differential signal line pairs, there is also a pair of CLK signals.
Under the conditions of high MIPI rate requirements, it is difficult for customers to debug. MIPI interfaces usually need to set initialization instructions, and there are many debugging problems required at the terminal end.
LVDS (Low Voltage Differential Signaling)
LVDS interface is a low-swing differential signal technology.
It can make the signal transmit at the rate of hundreds of Mbps on the differential line pair or balanced cable, and drive the output with low swing and low current to achieve low noise, low power consumption, and low Electromagnetic interference (EMI).
The LVDS signal is an electrical signal with a swing of ±350mV at a 1.2V DC bias level.
The interference between the same pair of differential – and + lines can cancel each other, so the anti-interference ability is strong.
LVDS is a current drive, and the voltage is obtained by placing a load on the receiving end. When the current flows in the forward direction, the output of the receiving end is 1, otherwise, it is 0.
Given its advantage, the LVDS interface usually applies on large screens, especially in industrial equipment and the automotive industry.
It can only transmit video data.
The LVDS interface offers three modes of data synchronization:
- VSYNC (Vertical Synchronization)
- HSYNC (Horizontal Synchronization)
- DE (Data Enable)
In terms of the Interface channel, there are 3，4，8 lanes.
Interface definition example of LVDS 4 lane:
The table above shows LVDS 4 lanes. In addition to 4 sets of LVDS differential signal line pairs, there is also a pair of CLK signals.
The LVDS interface usually has a programmed initialization code. It is the same as the RGB interface. If it needs to be initialized, you need to pull out the SPI port to set it. That is, LVDS+SPI. The power supply voltage and IO voltage are 3.3V.
EDP (Embedded Display Port)
The EDP interface is a digital interface based on the display port 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.
For instance, to drive a display with a resolution of 1440*900 pixels or above, it needs 8-lane LVDS. While using the EDP interface instead, it only needs 2 pairs of signal lines if the resolution is below 1600*900 pixels.
EDP interface is commonly embedded in tablets, notebooks, computers, and large-scale high-resolution displays.
The EDP interface is mainly composed of three signals:
- Main Link (The main channel. It is used to transmit various types of video and audio data)
- AUX CH (The auxiliary channel. It is used to transmit data, link management, and device control signals with low bandwidth requirements)
- HPD ( The hot plug detection channel )
Main Link consists of 1 to 4 pairs of data lines, each pair of data lines is a pair of differential lines.
For an LCD screen, the Main Link requires several pairs of data lines, which depend on the resolution and color bits of the screen.
Interface definition example of EDP:
Every terminal device is designed for a certain purpose. Thus, it will need some specific configuration, which has decided the requirement of display somehow.
To accommodate the different signals and interfaces due to the support limit of the driver, it needs an additional LCD converter or controller board to bridge the display to the motherboard, the common conversion such as RBG to LVBS, VGA, and CVBS.
Regardless of the interface type, you might need to support your terminal project, Tailor Pixels has the product development team ready to help.
There are other common display interfaces you may have interest