Every PC user sooner or later is faced with connecting his laptop or personal computer to the monitor using a variety of cables and connectors. All of them differ among themselves by structure, picture quality and maximum allowable cable length. In the 90s, a 15-pin VGA connector was used to connect CRT monitors, which gave good picture for that time. Over time, the resolution that VGA gives out became insufficient and it was replaced by a new 17 (17-29) pin DVI interface with the ability to display a much higher resolution due to its more bandwidth.
DVI connector
Large companies have joined forces to develop the Digital Visual Interface (DVI). It was jointly decided that it was not expedient to convert the signal twice. As a result, the developers came to the decision to create a single digital interface that can display the original image without unnecessary changes and loss of quality.
Basic principle of work interface is new technology TMDS data encoding protocol. The information previously implemented by the protocol is sequentially transmitted to the device.
The interface allows you to achieve a resolution of 1920x1080 at a frequency of 60 Hz. Such parameters can be achieved throughput 1.65 Gb / s and this is when using a single TMDS connection. If two connections are used, then the speed will increase to 2 Gb / s. At such high rates, DVI is head and shoulders above its predecessors.
For simple user to explain why the Digital Visual Interface is so good, you can only say that it is a digital video interface. It will not be difficult to distinguish it from its analog predecessor - the connectors are always white, which makes it impossible to confuse it with others. The shape and more pins are also a characteristic feature of the interface.
The interface cable is limited in length, like other connectors, its maximum length is no more than 10 m, which is 7 meters more than VGA.
Main types and differences
In addition to the characteristic differences from other interfaces, the Digital Visual Interface also differs from each other. The main differences between them are the number of channels and the availability of transmission capabilities. analog signal... Let's consider the popular variations in more detail:
To summarize the difference between the connectors, you can simply - the letter D indicates the presence of only a digital signal, the letter A - only analog, the letter I indicates the presence of both types of signal. 
In the case when the video card has a Digital Visual Interface output, and only VGA adapters are suitable on the monitor. When purchasing adapters, you need to understand the difference between DVI-I and DVI-D, the former will be able to transmit the signal to VGA since there is an analog channel, but the second does not have an analog communication channel and it will not work to transmit the image through it through the adapter, for this they use special expensive converters.
In addition to DVI-VGA and VGA-DVI adapters, there are other DVI-HDMI, HDMI-DVI, DVI-DisplayPort, DisplayPort-DVI, all of them transfer a digital signal between themselves and there should be no problems with connection.
Disadvantages of technology
The only significant drawback of the technology is cable length limitation... For example, when using a 15 m cable, the maximum resolution that can be achieved is 1280x1024, but if you use only a 5 meter cable, the resolution will increase to 1920x1200. If you want to connect your device to great distance without signal loss, you will have to use additional repeaters that will amplify the signal.
VGA connector
In 1987, Canon provided the world with a new VGA (Video Graphics Array) connector, which was installed on the video card of the same name. The capabilities of the technology were more than enough, because the original resolution was 640x480. Maximum possible resolution without loss of image quality, which is capable of producing Video Graphics Array, is 1280x1024. Despite the fact that more efficient interfaces have appeared for a long time, which supplant VGA from the market, many TVs and video devices are still equipped with this connector. The reason for the crowding out was the emergence of new monitors that require higher resolutions.
The connector has a 15-pin pinout and is marked in blue (with rare exceptions), which makes it easy to distinguish it from DVI (white). Maximum cable length for connection is limited to 3 m.
As technology advances, a new Super Video Graphics Array or SVGA standard has emerged that uses the same 15-pin connection as the Video Graphics Array but significantly surpasses it in technical terms. The main difference between SVGA and VGA is number of displayed colors, them in new version the interface has become 16 million, with 256 colors from the old one.
Main types
VGA connectors have three main types DDC1, DDC2, E-DDC:
- DDC1- allows the monitor to unilaterally transmit data with information about its characteristics to a computer. Then the video card determines this information on the cable and detects the DDC monitor connected to it
- DDC2- a specification of this type already allows the exchange of information in a two-way manner. First, the monitor transmits its data to the computer, after which the computer adjusts the necessary parameters for the connected monitor.
- E-DDC- represents the most efficient specification. Information about the connected monitor data was stored in the device memory.
All 15 contacts are arranged in 3 rows of 5 contacts. First three contacts are responsible for the transmission of an analog video signal of three different colors (1,2,3). Each of them has its own land- 6,7,8 respectively. 13 and 14 contacts are responsible for horizontal and vertical synchronization. In addition to video signal transmission, the interface has two-way communication with the monitor.
Interface pinout:
If we are talking about a mini VGA mini-connector (a reduced analogue with the same parameters), then the pinout will be as follows:
Extension cords
There are situations when the computer and the connected monitor or TV are in different rooms and a non-standard cable is required to connect them. You can buy it at any computer store, but there are two problems:
- too much high price cable - from $ 20 for 15 meters;
- rigidity standard cable, which becomes a big problem for a beautiful and correct installation in skirting boards. If, when installing the cable, you need to go through the wall, then the factory cable will obviously not help. you will have to drill a hole with a diameter of 40 mm.
In cases like this perfect solution will make the extension cord yourself. The usual twisted pair of 5 or 6 categories will come to the rescue in this. 
In terms of price, it significantly outperforms the factory Video Graphics Array extension cable, its price is about 15 rubles per meter, and its diameter is only 8 mm.
Using only 8 twisted pair pins, you can easily solder an extension cord, but you can do it even easier by buying a VGA to RJ-45 adapter in the store. 
DVI-D - DIY VGA adapter
It is impossible to find such an adapter. This is due to the fact that technologies use different ports and data types. If you look closely at the DVI-D pinout, you will notice that it has no contacts to carry the analog signal that VGA requires.
In this case, it can help converter DVI-D - VGA, which converts the digital signal from the Digital Visual Interface to analog. This is the only connection option.
Worth noting that if you break off 4 "extra pins" due to which the usual adapter is not inserted into the connector, then nothing will work anyway, since it is they who are responsible for transmitting the analog signal. 
Maximum cable length
All interfaces have a limitation on the maximum allowable cable length at which the signal quality is not lost. The longer the cable length, the worse the signal, and therefore the maximum resolution. The maximum length is different for each type, since the interfaces use different technologies and types of signals.
For DVI - 10, VGA - 3 m, HDMI - 10 m.
Difference between DVI and VGA
The main difference between these connectors is maximum resolution and picture quality... In addition, the Digital Visual Interface has from 17 to 29 pins, while the VGA is only 15. Another difference is the type of signals with which the interfaces work: for VGA it is analog, and for Digital Visual Interface it is digital. It is for this reason that VGA has to be converted twice, which significantly degrades the quality of the resulting image.
Which is better DVI or HDMI
Comparing these two interfaces, we can say about their certain equivalence. The big advantage of HDMI is that with just one cable, you can transfer both video and audio data, thereby reducing the number of wires that are plentiful in modern multimedia systems. The essential difference is maximum resolution, which at the moment HDMI can be 10240 × 5760.
Difference between VGA and HDMI
It is incorrect to compare these two interfaces due to their difference in creation time. HDMI is a fairly new connector that provides the user with an excellent picture and great sound in just one cable. The Video Graphics Array is now used mostly in older technology that is incompatible with new technologies.
Greetings to my readers and we continue to discuss Various types connectors used for video signal transmission. The subject of our conversation today will be the VGA connector, which is well known to many for its catchy blue color.
Some consider IBM to be the inventor of this connector, which in 1987 proposed using it to connect monitors to their PS / 2 computers.
Then, with the help of such a connector, called the Video Graphics Array (video-graphic array), an image of 640x480 pixels was transmitted (which also became known as the VGA format).
But in fact, the progenitor of this type of connector is a division of the ITT Corporation. Introduced in 1952 the concept of compact connectors with a large number of pins located inside the shield.
Its shape resembled an inverted D beech, which ensured the connection only in the right way. Thanks to the letter, these connectors are marked D-sub (subminiature).
Fifteen important contacts
But let's go back 30 years, when the VGA connector became ubiquitous in the computer industry (video cards, monitors). Its feature was the progressive transmission of analog video. Each of his 15 contacts was responsible for certain parameters:
- Separate RGB signals;
- Synchronization methods;
- Other control channels
In more detail, the standard pinout of contacts looks like this:
Brightness indicators were determined by changing the signal voltage within 0.7-1 V.
This layout, coupled with a stable component video interface, provided pretty decent picture quality with fast refresh rates. Potential inherent in this system, allowed you to reassign tasks for individual contacts. And also provide signal transmission for more advanced equipment. An additional benefit the connector was a system of its fixation with two screws, which ensures high reliability of the connection.
High potential connector
If at first the VGA connector was used to connect monitors with a CRT, then over time it began to be used in modern LCD screens with a resolution of 1280 × 1024 and a frame rate of up to 75 Hz. In fact, with the help of such a cable, a digital signal was transmitted. Which underwent double conversion (to analog and vice versa). With the appropriate quality of the connecting wire, the presence of a shielding braid and a short connection length, the transmitted picture was quite good.
Over time, a smaller version appeared - mini VGA, which was used in compact equipment and laptops.
And the main standard size of the connector, due to its high reliability, has become in demand in systems industrial automation... There are also numerous adapters for connecting a VGA plug to other types of connectors (RCA DVI-I, HDMI).
In addition, the analog signal allows you to simultaneously broadcast the image to two monitors. What does the cable look like VGA splitter, for such switching you can see in the picture.
Of course, today, for video with the maximum resolution, the capabilities of analog VGA are no longer enough and it is necessary to switch to digital broadcasting of the stream using, or even better, HDMI or with the highest data transfer rate. This idea is actively promoted by Intel and AMD. Those who officially announced that from 2015 their products will not support VGA.
That's all the information about VGA connectors. Finally, I want to recommend that you revise the used monitor and TV for refusal from analog cables in favor of digital ones. And I am sure that there will be such an opportunity.
That's all, see you soon on the pages of my new articles.
DVI is a standard for an interface and a corresponding connector used to transfer video images to digital display devices such as LCD monitors, televisions and projectors.
Since the signal transmitted via the DVI cable is digital and does not need double conversion, the maximum length of the cable used should not exceed 5 meters.
The DVI video interface can be of two types, 24-pin and 29-pin.
DVI-D 24-pin is designed for digital interface. Only a digital code is sent to its pins
DVI-I 29-pin connector, the difference is that it also supports analog signal transmission
VGA connector is outdated analog interface, developed in 1987 and intended for connecting analog monitors, but is still used today.
VGA - Transmits three signals for chroma, luma and sync. Its pinout and the purpose of each pin:
Knowing the pinout of these connectors, you can easily solder a DVI-VGA or VGA-DVI adapter.
Composite video input / output (RCA), it is an analog video input - output, is widely used in video equipment as universal remedy switching. Often called "Asian" or "Tulip". There are practically two separate coaxial connectors, they can be seen on the back of almost any VCR, TV, DVD-player. The standard is purely analog, carries a standard composite video signal. The main advantage of the interface is simplicity and low cost. Chroma and luminance signals are transmitted over the same wire. This does not allow for a very clear image, so the real resolution is in the region of 250-280 lines. The maximum cable length can be 20-30 meters.
These connectors can be present in a PC on a video card or an internal TV tuner card for receiving and transmitting an analog signal, for supplying a picture to the screen of a conventional TV, for recording the generated video signal to a VCR, for transmitting a signal from an analog video source to a video capture card.
S-Video (or S-VHS), another analog connector widely used now in video equipment. The signals of chromaticity and luminance go along separate veins, and do not interfere with each other at all. Therefore, a picture with a resolution of 400-500 lines can be obtained.
Table 1 Designation of VGA connector pins
| Output | Name | Direction | Description |
|---|---|---|---|
| 1 | RED | Red video (75 Ohm, 0.7 V) | |
| 2 | GREEN | Green video (75 Ohm, 0.7 V) | |
| 3 | BLUE | Blue videos (75 Ohm, 0.7 V) | |
| 4 | RES | Reserved | |
| 5 | GND | Earth | |
| 6 | RGND | Land for red | |
| 7 | GGND | Land for green | |
| 8 | BGND | Land for blue | |
| 9 | KEY | - | Not used |
| 10 | SGND | Sync signal ground | |
| 11 | ID0 | Not used | |
| 12 | SDA | I 2 C bidirectional data transmission | |
| 13 | HSYNC or CSYNC | Horizontal sync | |
| 14 | VSYNC | Vertical sync | |
| 15 | SCL | I 2 C synchro signal |
Let's drop I2C and there are only a few pins left. All the grounds can be connected together, as a result there will be 3 RGB colors, analog voltage from 0 to 0.7 V is applied to these pins, the higher the voltage at the color input, the more "saturated" this color. 0.7V on all 3 pins will give the brightest white color the monitor is capable of. Thus, you can get almost any color by mixing 3 components. For the sake of simplicity, I will supply either 0 or 0.7 V to each of the pins. If you want a wide variety of colors, you need to use digital-to-analog DAC converters. You can compose it yourself using a resistor matrix. Or get a special microcircuit, for example: AD664
The TTL signal levels are applied to the vertical and horizontal sync pins.
- Logic zero level, no more than +0.8 V
- Logic unit level, not less than +2.4 V
In general, they work stably with MK at 3.3 V and 5 V.
When powered by 3.3 V (standard FPGA voltage) (logic 1 ≈ 3.3 V)
the color inputs are fed through 270 ohm resistors.
As we remember, the input impedance of VGA color inputs is 75 Ohm.
Let's calculate the maximum voltage:
3.3 * 75 / (75 + 270) = 0.717V
Slightly higher, but works without problems.
When powered from 5 V, resistors with a nominal value are required:
R = 3.3 * 75 / 0.7 - 75 = 460 ≈ 470 Ohm
It remains to find out at what moments to apply ones and noughts to these conclusions.
The image resolution and refresh rate are determined by the timing of the sync pulses. During sync pulses on RGB pins, it should be 0 V.
Video data of the 1st line - horizontal synchro pulse - video data of the 2nd line - horizontal synchro pulse - video data of the 3rd line - ********************* - drawing the last line is a large vertical sync pulse (along with the horizontal one) - All over again.
Consider the parameters for a resolution of 640 x 480 @ 60 Hz
Table 2 Frequency parameters of the VGA interface
Table 3 timing parameters for the horizontal line
Table 3 timing parameters for 1 frame
It is not necessary to use exactly the same values as in the table, as long as they are close enough. Negative vertical and horizontal sync pulses are used for this resolution; this may not be the same for other resolutions.
You may notice that the vertical sync frequency sometimes does not coincide with the refresh rate of the screen. LCD monitors have replaced CRT monitors, which have replaced large CRT televisions. When it became possible to display a color image on the screen, American engineers had a problem, the sound transmission frequency standard which they chose "does not match" (causes interference) with 60 Hz. The standard for the frequency was 44.056 kHz. But they found out that changing the frequency by 0.1% would fix it, and so on. the sound transmission standard was already generally accepted, they reduced the refresh rate of the screen.
60 * 0.999 = 59.94
Because many values were adopted even then, the manufacturers got used to them and continue to use them, if you change the standard now, you have to do too much work, not counting the fact that many devices may simply stop working with new standards.
You can read more about this and
I do not know the reason for the differences in other values and why it was impossible to make the time intervals multiples of 10, 5, or at least 2.
The tables show that there is a time when nothing is displayed on the screen, this is done for synchronization, it can be imagined that our drawing beam (previously the image was displayed by an electron beam) goes beyond the boundaries of the screen. You also need to wait for a few empty lines that go under the visible screen.
 |
| Rice. 8 Screen with sync zones (Blanking Time) |
It is easier to calculate and implement the time of 1 pixel and then adjust everything to it, sometimes just the pixel frequency and other values in pixels are indicated.
In principle, this is all you need to know to draw on VGA monitor, it remains to program (or in any other way) the digital device and try to display the image.
The TV works almost the same, but there is only "1 wire", which means all signals are connected together, if the color is not so important, then the principle is the same.
Let's try to display the image and look at the waveform of the signal.
I have a ready test program for FPGA from here which outputs this image:
Let's consider an oscillogram. From top to bottom in order are: Red, Green, Blue, Horizontal sync, Vertical sync.
1 frame is displayed here, you can guess how the image will look, since each strip consists of impulses (if you zoom in, there are zones where 1 is constant, but not long in the whole line), then there will be no one-color lines. If you break the signals into columns, you can see that there are lines on which the intervals are only red or green.
The values I used are:
Entire frame (O) - 16.69284 ms
Vertical sync pulse width (P) - 64.08 μs
1 line (A) - 31.9176 μs
Horizontal sync pulse width (B) - 3.84 μs
Pixel frequency - 25 MHz
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