Do you know what interfaces LCD and CTP have?And how each interface is used?

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Do you know what interfaces LCD and CTP have?And how each interface is used?

There are many ways to interface an MCU (Microcontroller Unit) or MPU (Microprocessor Unit) or CPU (Central Processing Unit) with an LCD.

Figure 1 Connection between MCU and LCD

Figure 1 Connection between MCU and LCD

LCD driving waveform

The LCD cannot be driven with DC (direct current), it must be driven with AC (alternating current), and the total current must be zero. Otherwise, the liquid crystal material will be damaged sooner or later.

Figure 2 LCD driving waveform

Figure 2 LCD driving waveform

LCD controller and driver

There are two types of driver ICs, universal drivers and segment drivers. A universal driver outputs a signal to create a row or number of rows. Segment drivers output the necessary signals to create characters or columns.

The controller IC receives data written in ASCII or JIS code from the MPU and stores the data in RAM. This data is then converted into serial character mode and transferred to the LCD driver IC.

Driver/controller ICs are probably the most common among graphics modules. This IC receives data from MPU and stores it in RAM. Additionally, it accepts commands directly from the MPU for common and segment drivers.

Parallel and serial interfaces

Parallel interfaces can transmit multiple bits of data simultaneously, depending on the data bit width.

The serial interface can transmit one bit of data at a time

Microcontroller/parallel interface

MCU interfaces include 6800 and 8080. 8080 is much more popular than 6800. The MCU interface generally consists of 4/8/9/16bits data (such as DB0, DB1,..., DB7; Note: 8bits is the most popular bit width), CS (chip select), RS (data register or instruction register selection) ), RD (read enable), WR (write enable).

Advantages: simple

Disadvantages: Requires memory, limited speed.

For Mono characters, graphics, small TFT (less than 3.5")

Figure 3 MCU Parallel Interface

Figure 3 MCU/Parallel Interface

Serial interface

Serial interfaces include: I2C, SPI, RS232

Pros: Fewer connections, lower hardware costs

Disadvantages: Software is more complex

SPI interface

SPI (Serial Peripheral Interface bus) consists of the following 4 lines:

SCLK: serial clock (output from host);

moxi; master output, slave input (slave master output);

miso; master input, slave output (slave slave output);

SS: Slave selection

For singular, character, graphic LCD, small TFT, some CTP

Figure 4 4-wire SPI interface

Figure 4 4-wire SPI interface

Figure 5 3-wire SPI interface

Figure 5 3-wire SPI interface

IIC (I²C) interface

I²C (Inter Integrated Circuit) consists of the following 2 connections.

SCL (Serial Clock Line),

SDA (Serial Data and Address Line).

For use with singular, character, graphic LCDs, small TFTs, and most capacitive touch screens.

Figure 6 IIC (I²C) interface

Figure 6 IIC (I²C) interface

RGB interface

The RGB interface is often used to control large high-resolution LCD displays. It includes 6/16/18-bit data (such as R0, R1,,,G0,G1,,,B0,B1,,,,), VSYNC (vertical synchronization), HSYNC (horizontal synchronization).

The advantage is that R, G, and B data are written directly to the LCD without GRAM and are fast. Typically used for large, high-resolution LCD displays.

The disadvantage is that controlling the LCD is more complicated and requires more data lines than the MCU interface.

Application: Medium TFT (3.5” to 8”)

RGB interface includes 24-bit, 18-bit, and 16-bit.

Figure 7 RGB interface

Figure 7 RGB interface

LVDS interface

LVDS (Low Voltage Differential Signaling) is an electronic digital signaling standard that can run at very high speeds over inexpensive twisted pair copper cables.

Most commonly used for large LCD Displays (>7 inch).

Figure 9 LVDS interface example

Figure 8 LVDS interface example

MIPI DSI interface

MIPI (Mobile Industry Processor Interface) Alliance, DSI (Display Serial Interface)

Designed to reduce the cost of display controllers in mobile devices. It typically targets LCD and similar display technologies. It defines the serial bus and communication protocol between the host (source of image data) and device (destination of image data)

The MIPI interface is becoming more and more popular.

Figure 9 MIPI interface example

Figure 9 MIPI interface example

eDP interface

DisplayPort (DP) is a digital display interface developed by an alliance of PC and chip manufacturers and standardized by the Video Electronics Standards Association (VESA). This interface is mainly used to connect video sources to display devices such as computer monitors, and can also carry various forms of data such as audio and USB.

DisplayPort is designed to replace VGA, DVI, and FPD-Link. The interface is backwards compatible with other interfaces such as HDMI and DVI through the use of active or passive adapters. It is mainly used for larger size and higher resolution displays.

Figure 10 eDP interface

Figure 10 eDP interface

Figure 10 eDP interface

UART interface

A Universal Asynchronous Receiver/Transmitter (UART) is the circuit block responsible for implementing serial communications. Essentially, the UART acts as an intermediary between parallel and serial interfaces. On one end of the UART is a bus of eight or so data lines (plus some control pins), and on the other end are two serial lines - RX and TX.

Figure 11 URAT interface

Figure 11 URAT interface

USB interface

Universal Serial Bus (USB) is a universal interface that enables communication between a device and a host controller, such as a personal computer (PC). It connects peripherals such as digital cameras, mice, keyboards, printers, scanners, media devices, external hard drives, and flash drives. The USB specification has had four generations: USB 1.x, USB 2.0, USB 3.x, and USB4.

It is widely used for capacitive touch screen connections.

Figure 12 USB interface

Figure 12 USB interface

HDMI interface

HDMI (High Definition Multimedia Interface) is a proprietary audio/video interface used to transmit uncompressed video data and compressed or uncompressed digital audio data from an HDMI-compatible source device (such as a display controller) to a compatible Computer monitor, video projector, digital television or digital audio equipment. HDMI is the digital replacement for the analog video standard.

As color TFT LCDs become more popular, HDMI is becoming more and more popular in the display industry.

Figure 13 HDMI interface

Figure 13 HDMI interface

Figure 13 HDMI interface

RS232

RS232 is a standard protocol for serial communication, used to connect computers and their peripheral devices to exchange serial data between them. Because it gets the voltage of the path used for data exchange between devices.

RS232 includes the following connections:

RX

VSS signal ground

VDD +5v

Figure 14 RS232 interface

Figure 14 RS232 interface

Compared with later interfaces such as RS-422, RS-485 and Ethernet, RS-232 has lower transmission speed, shorter maximum cable length, larger voltage swing, larger standard connector, and no Multipoint capabilities and limited multipoint capabilities. In modern personal computers, USB has replaced RS-232 in most of its peripheral interface roles. Very few computers today are equipped with RS-232 ports, so you must use an external USB to RS-232 converter or an internal expansion card with one or more serial ports to connect RS-232 peripherals. Despite this, due to its simplicity and past ubiquity, the RS-232 interface is still used - particularly in industrial machines, network equipment, and scientific instruments where short-range, point-to-point, low-speed wired data connections are sufficient.

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