What model does vga belong to?

vga is a standard model of computer display. After the advent of the computer, this interface became the interface for connecting the host and the monitor. The vga interface is usually blue and looks similar to a capital letter D. This interface is a product of the analog information age. There are 15 pinholes in the interface, divided into three rows.

#The operating environment of this article: Windows 10 system, dell g3 computer.

vga is a standard model of computer display. To be precise, the vga interface is an analog interface. After the advent of the computer, this interface became the interface for connecting the host and the monitor. The vga interface is generally blue and looks similar to a capital letter D. This interface It is a product of the analog information age. Its interface has 15 pinholes divided into three rows. As far as the market is concerned, there are still quite a few devices with this kind of interface, but they are already gradually becoming outdated, so they will basically be eliminated. The essence of this interface is an analog interface, which can only accept the input of some analog signals. Most LCD monitors now directly receive digital signals, but many low-end machines still use this interface.

Display mode:

VGA originally referred to the display mode of monitor 640X480.

The application of VGA technology is mainly based on computers, notebooks and other devices with VGA display cards. However, in some devices that require display of color high-resolution images and do not need to use a computer, VGA technology is rarely used. See.

For some embedded VGA display systems, VGA image display and control can be achieved without using a VGA display card and computer. The system has the advantages of low cost, simple structure, and flexible application. It can be widely used in advertising and prompt information display in public places such as supermarkets, stations, and airports. It can also be used to display operating information in the production process of factory workshops. It can also Used in daily life in the form of multimedia.

Principle:

Display and timing

The general VGA display card system mainly consists of control circuit, display buffer area and video BIOS (Basic Input Output System (Basic Input Output System) program consists of three parts. The control circuit mainly completes functions such as timing generation, display buffer data operation, main clock selection, and D/A (Digital to Analog) conversion. The display buffer provides display data cache space; the video BIOS serves as the control program. Solidified in the ROM (Read-Only Memory) of the display card.

VGA Timing Analysis

Through the analysis of the basic working principle of the VGA display card, it can be seen that to achieve VGA display, we must solve problems such as data sources, data storage, and timing implementation. The key is how to implement it. VGA timing. Both row timing and frame timing need to generate four parts: synchronization pulse (Sync a), display back edge (Back porch b), display timing segment (Display interval c) and display front edge (Front porch d).

VGA Timing Implementation

First, determine the main clock frequency based on the refresh frequency, then calculate the total number of row cycles based on the main clock frequency and image resolution, and then add a, The time of each timing segment b, c, and d is converted into the number of clock cycles according to the frequency of the main counting pulse source. In CPLD, counters and RS flip-flops are used to generate pulse signals of different widths and periods based on the calculated number of clock cycles in each time sequence, and then their logical combination is used to form a, b, c, d in Figure 2 Each timing segment and the blank signal BLANK and synchronization signal SYNC of the D/A converter.

SRAM address

The main clock serves as the pixel count pulse signal, and also provides the read signal of the display SRAM and the D/A conversion clock. The output end of the counter it drives serves as the low bit of the read SRAM. address. The row synchronization signal is used as the row number counting pulse signal, and the output end of the counter it drives is used as the high-order address for reading the SRAM. Since two pieces of SRAM are used, the highest bit address is used as the chip select of the SRAM. Since there is a certain time delay when the signal passes through the internal logic device of the CPLD, when the CPLD generates the address and read signals to read the data, the read signal, address signal and data signal cannot meet the timing requirements of the SRAM to read the data. Hardware circuits can be used to make certain timing adjustments to the read signals so that the timing requirements for reading SRAM and inputting data to the DAC can be met between each signal.

Data

If VGA displays a true color BMP image, the three components of R, G, and B are required to be 8 bits each, that is, 24 bits represent a pixel value, and in many cases 32 bits are used. Represents a pixel value. In order to save the storage space of the video memory, high-color images can be used, that is, each pixel value is represented by 16 bits, and the three components of R, G, and B use 5, 6, and 5 bits respectively, which is half the amount of data compared with true color images. , and at the same time can meet the display effect.

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