In this article, we try to organize the kinds of display interfaces, and how they differ from each other. There is the outline.
- Display Interface
- Display interface and protocol
- External Interface
- Internal Interface and Application：SPI,I2C,RGB,LVDS,MDDI,MIPI
We divide interfaces into internal and external interfaces in LCD modules. Internal means are used inside the device; they usually are embedded interfaces that are not visible, and we do not have access to them as the users of the device. External interfaces, on the other hand, are connected to the device using a cable.
Display interface and protocol
A protocol defines the rules of information exchange, where the interface is the medium. The example here will be language. When I use my voice to communicate with other people, my voice is an interface. Over this interface, my voice is being sent to other people’s ears, and the protocol is the language used In this article we will talk only about interfaces, and how to connect devices to each other; we will talk about protocols in the next article.
There are various connection types for interfacing a computer or video device to a display such as a computer monitor, projector, or TV. The most common types that you will see are HDMI, USB-C, and Thunderbolt 3.
Internal Interface and Application
Serial Peripheral Interface (SPI)
Serial Peripheral Interface (SPI) was developed by Motorola in the mid-1980s and has become a de-facto standard. It’s a synchronous serial data protocol used by microcontrollers for communicating with one or more peripheral devices quickly over short distances. Such as flash memory, sensors, Real-Time Clocks, analog-to-digital converters, and more. Because there is no protocol overhead, the transmission runs at relatively high speeds. SPI is a great option for small, low-resolution displays including PMOLEDs and smaller LCDs.
Inter-integrated Circuit (I2C)
Philips Semiconductors invented Inter-integrated Circuit(I2C) in 1982. It utilizes a multi-master, multi-slave, single-ended, serial computer bus system. Engineers developed I2C for simple peripherals on PCs, like keyboards and mice to then later apply it to displays. Like SPI, it only works for short distances within a device and uses an asynchronous serial port. What sets I2C apart from SPI is that it can support up to 1008 slaves and only requires two wires, a serial clock (SCL), and serial data (SDA). Like SPI, I2C also works well with PMOLEDs and smaller LCDs. Many display systems transfer the touch sensor data through I2C.
Red Green Blue (RGB)
The RGB interface is a special parallel interface that transmits up to 8-bits of red, green, and blue data to each pixel. The number of bits transmitted per clock cycle is dependent on the setup and programming of the display. It can vary from 16 to 18 or 24 data pins that are used for each of the RGB signals. RGB does not typically have internal DDRAM memory and the data is written directly to the device from the GPIO pins. RGB is rather low speed and not very immune to noise, so it is used for the smaller size displays and low resolution.
Low-voltage Differential Signaling (LVDS)
Low-voltage differential signaling(LVDS) was developed by NS in 1994. It is a high-speed, long-distance digital interface for serial communication (sending one bit at a time) over two copper wires (differential) that are placed at 180 degrees from each other. This configuration reduces noise emission by making the noise more findable and filterable. LVDS is used in applications such as HD displays, infotainment systems, industrial cameras, and the transmission of large amounts of data.
Mobile Display Digital Interface (MDDI)
Mobile Display Digital Interface (MDDI) is a high-speed digital interface developed by Qualcomm to interconnect the upper and lower clamshell in a flip phone. The MDDI solution supports variable data rates of up to 3.2 Gbit/s and decreases the number of signals that connect the digital baseband controller with the LCD and camera.
Mobile Industry Processor Interface (MIPI)
Mobile Industry Processor Interface (MIPI) is a newer technology that is managed by the MIPI Alliance and has become a popular choice among wearable and mobile developers. MIPI uses similar differential signaling to LVDS by using a clock pair and one to eight pairs of data called lanes. MIPI supports a complex protocol that allows high speed and low power modes, as well as the ability to read data back from the display at lower rates. There are several versions of MIPI for different applications, MIPI DSI being the one for displays.