Design of vga/lcd display controller system based on FPGA (Part 1)

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Today, I bring you FPGA Of VGA/LCD Display controller design , Because of the long space , It is divided into three parts . Today I bring the first one , Part 1 ,VGA Display principle and VGA/LCD Display the basic framework of the controller , Don't talk much , Loading .

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Reading guide

VGA (Video Graphics Array) Video graphics array , yes IBM On 1987 Annual follow PS/2 machine (PersonalSystem 2) A video transmission standard using analog signals . This standard is very outdated for today's PC market . But at that time, it had high resolution 、 The display speed is fast 、 Rich colors, etc , It has been widely used in the field of color display , It is a low standard supported by many manufacturers .

LCD （ Liquid Crystal Display For short ） Liquid crystal display .LCD The structure is to place a liquid crystal cell between two parallel glass substrates , The lower base plate is arranged on the glass TFT（ Thin film transistor ）, A color filter is arranged on the upper substrate glass , adopt TFT The rotation direction of liquid crystal molecules is controlled by changing the signal and voltage on the liquid crystal , So as to control whether the polarized light of each pixel is emitted or not and achieve the purpose of display . According to the different backlights ,LCD Can be divided into CCFL A display and a LED There are two types of monitors .LCD Has replaced CRT The mainstream , Prices have also fallen a lot , And has been fully popularized .

In the previous article, I introduced how to get 、 Process the video signal provided by the camera , In practical application, the processed signals need to be displayed on the display . This process is opposite to that in signal processing , The composition of digital signals according to the system of TV signals conforms to the time sequence 、 Signal with required format , And add various synchronization signals for control . This article will pass FPGA Achieve one VGA/LCD Displays an instance of the controller , And the implementation process is introduced in detail .

The first content abstract ： Introduction VGA Display principle , Including the principle of image display 、 Common video display standards ; It will also introduce VGA/LCD Display the basic framework of the controller and other related contents .

One 、VGA Display principle

In the design VGA Display the implementation process of the controller , The first thing to understand is VGA Display principle of .

1.1 Image display principle

VGA The display controller controls the image signal to be transmitted to the display through the cable and displayed . The current display technology mainly includes two types ：CRT（Cathode Ray Tube, crt ） and LCD（Liquid Crystal Display, LCD screen ）.CRT The electron beam of the electron gun is controlled to scan line by line and point by point by frame synchronization signal and line synchronization signal , Strike an electron on a fluorescent spot , Make it glow .

Through the role of visual persistence , What you see is a complete picture .LCD And CRT similar , It is also a dynamic scanning . but CRT It's analog , Controlled by circuit , The electron beam can move freely ; and LCD It's digital , There is only a fixed current path , So you can only scan line by line through the circuit matrix , Not point by point , That is, all points on a line work at the same time .CRT The connection diagram of the display is shown in the figure 1 Shown .

chart 1 CRT Schematic diagram of display connection

VGA Display controller control CRT The process of displaying the image is shown in Figure 2 Shown .

chart 2 VGA Display controller control CRT Block diagram of the display

The scanning process of the electron gun is synchronized 、 Field synchronization and other control signals , Including horizontal scanning 、 Horizontal retrace 、 Vertical scanning 、 Vertical retrace, etc , Pictured 3 Shown .

chart 3 Scanning process

1.2 Common video display standards

Video display standards have been gradually improved with the continuous progress of display technology and technology ：

• The first to display characters was MDA standard （Monochrome Display Adapter, Monochrome display adapter interface ）, Only character display mode is supported , Only black and white , Display specifications 80 Column ×25 That's ok , A resolution of 720×350.
• CGA standard （Color Graphic Adapter, Color graphics adapter interface ）, Support color image mode , Display specifications from 40 Column ×25 Row to 80 Column ×25 That's ok , Colors range from black and white to 16 color .
• EGA standard （Enhanced Graphics Adapter, Enhanced graphics adapter interface ）, In addition to compatibility MDA、CGA Out of standard , Enhanced mode is also supported , The graphic display specifications are from 320×200 To 640×350, Colors range from black and white to 16 color .
• VGA standard （Video Graphies Array, Video graphics array ）, In addition to being compatible with the above standards , It also includes QVGA、VGA、SVGA And so on , Support from the 640×480 To 800×600 And other higher display specifications . What is commonly used at present is VGA standard , The following examples will describe VGA Standard display controller .

Two 、VGA/LCD Display the basic framework of the controller

VGA The program framework of the display controller is shown in the figure 4 Shown . This VGA/LCD The display controller provides access to CRT、LCD Support for , It is suitable for the development of embedded system .

chart 8-4 VGA Display controller program framework

VGA The program framework of the display controller includes the following main parts ：

• Color lookup table The color lookup table saves 256 Color resolution R、G、B All possible colors , So it's a piece 256×24 Bit static RAM District , Each pixel consists of R、G、B Each color 8 Bit data composition , The program includes two such color lookup tables , altogether 512×24 position .
• register Including all kinds of control required by the whole program 、 Status register .
• Color processor Used to convert the received pixel data into RGB Color information .
• Cursor processor Used to convert saved cursor information into visible cursor .
• Output FIFO Used to ensure continuous data flow output to VGA perhaps LCD On the monitor .
• Video timing generator Used to generate various synchronization signals required for display , Such as field synchronization 、 Line synchronization 、 Composite synchronous signal, etc .

This is the end of this article , The next one is based on FPGA Of VGA/LCD Display controller design （ in ）,VGA/LCD Implementation of display controller program , Including top-level programs 、 Color lookup table 、 Color processor 、 Cursor processor 、 Video timing generator and output FIFO And so on .