Despite the widespread distribution of digital networks, analog data transmission channels are still used. There are several reasons for this.

In industrial automation systems, there are a large number of devices designed and manufactured many years ago that use analog data transmission channels. These can be sensors, actuators (valves, pumps), as well as recording devices (recorders). Replacement of this equipment is slow and requires a very large capital investment. In addition, the transfer of an enterprise entirely to digital networks means a one-step replacement of almost all equipment and information cable networks. Such a large-scale reconstruction requires not only huge funds, but also stopping the production process, which in many cases is unacceptable. Therefore, when creating or modernizing automatic control systems, it is necessary to use analog data transmission channels to receive information from sensors and transfer control to actuators.

Benefits

The main advantage of using a 4… 20 mA current loop as a data transfer interface from sensors is the use of only two wires for connection to the data acquisition system. In addition, unlike digital interfaces, no additional hardware or software is required to implement a standard communication protocol or additional configuration (for example, address programming) during installation.

Current or voltage

Figure: one.

At the same time, the use of analog interfaces with intelligent sensors (into which microcontrollers are built for signal preprocessing) or actuators with an analog interface, which must be controlled by a digital controller, requires the use of a digital-to-analog converter. Considering that in various cases both current and potential interfaces can be used, to simplify the circuit and reduce its cost, it is advisable to choose a DAC chip capable of providing both types of output signals without additional elements.

This is the microcircuit of a specialized sixteen-bit digital-to-analog converter MAX5661 (see fig. 2).

Figure: 2.

The capabilities of the microcircuit sharply distinguish it from similar devices. It should be noted that it is capable of generating both current signals in the range of 0 ... 20/4 ... 20 mA, and potential (including a 4-wire circuit with compensation for the resistance of connecting wires) with an amplitude of up to ± 10 V, and the initial zero offset does not exceed 0.1%, and the total error is not more than 0.3% of the full scale. The transfer characteristic of the DAC has guaranteed monotonicity, which is extremely important for closed-loop controllers.

When designing the microcircuit, it was decided to use an external reference voltage source of 4.096 V. This is due to the fact that during the operation of the DAC, the crystal temperature can change significantly, which can significantly affect the parameters of the built-in reference voltage and significantly reduce the accuracy of the system as a whole. This temperature change is especially pronounced at the current output at high supply voltage (which can be up to 40 V) and low load resistance, since the output transistor of the voltage-current converter is built into the microcircuit. With a small bit DAC, this would not matter much, however, for 16-bit systems, moving the reference voltage source outside the main crystal can significantly improve the accuracy characteristics.

Another advantage of the described IC can be considered the use of a high-speed (up to 10 MHz) serial SPI / QSPI / Microwire interface for communication with the control microcontroller, and it is possible to connect several microcircuits in series (Daisy Chaining). There is a FAULT output, which becomes active when the voltage output is short-circuited or the current loop is broken. Information about the alarm state of the outputs is also available via the serial interface. The output stages of the microcircuit can be configured using software or using special inputs that are connected to ground or to the supply voltage (+5 V nom.).

The MAX5661 microcircuit also has two inputs for asynchronous control. One of them - CLR - allows you to either reset the DAC or load a preset value (determined by software). Another - LDAC - allows you to load the value of the input data register. Both inputs can be used for simultaneous asynchronous control of several microcircuits.

Conclusion

Analog information transmission has retained its popularity in the traditionally conservative industrial field of application. This is confirmed by the fact that chip manufacturers continue to offer new integrated solutions for its implementation.

Obtaining technical information, ordering samples, delivery -
e-mail:

Data transfer begins with a printer readiness check - Busy line status. The data strobe can be short - fractions of a microsecond, and the port ends its formation, not paying attention to the signal Busy... During the strobe, the data must be valid. Acknowledgment of receipt of a byte (character) is a signal Ack #, which is generated after receiving a strobe after an indefinite time (during this time, the printer can perform some long-term operation, for example, paper feed). Pulse Ack # is a printer request to receive the next byte, it is used to generate an interrupt signal from the printer port. If interrupts are not used, then the signal Ack # ignored and the entire exchange is controlled by a pair of signals Strobe # and Busy... The printer can report its state to the port over the lines Select, Error #, PaperEnd - from them you can determine if the printer is on, if it is working properly and if there is paper By shaping a pulse on the line Init # the printer can be initialized (it will also clear its entire data buffer). Automatic line feed is usually not used, and the signal AutoLF # has a high level. Signal SelectIn # allows you to logically disconnect the printer from the interface.
Through the parallel port (LPT), the Centronics protocol can be implemented purely in software using the standard port mode ( SPP), reaching a transfer rate of up to 150 Kbytes / s with a full processor load. Thanks to the "advanced" port modes, the protocol can be implemented in hardware ( Fast Centronics), while the speed up to 2 MB / s is achieved with a lower processor load.
Most modern printers with a parallel interface also support the IEEE 1284 standard, in which ECP is the optimal transmission mode (see section 1.3.4).
A Centronics cable is required to connect to the printer and is suitable for all parallel modes. The simplest version of the cable - 18-wire with straight wires - can be used for SPP operation. With a length of more than 2 m, it is desirable that at least the lines Strobe # and Busy were intertwined with separate common wires. For high-speed modes (Fast Centronics, ECP), such a cable may be unsuitable - irregular transmission errors are possible that occur only with certain sequences of transmitted codes. There are Centronics cables that do not have a connection between pin 17 of the PC connector and pin 36 of the printer connector. If you try to connect a 1284 printer with this cable, you will be prompted to use a "bi-directional cable". The printer is unable to tell the system about extended mode support, as the printer driver is counting on. Another manifestation of a missing connection is the printer “freezing” after finishing printing a job from Windows. This connection can be organized by soldering an additional wire or simply replacing the cable.
Ribbon cables have good electrical properties, in which signal circuits (control signals) alternate with common wires. But their use as an external interface is impractical (no second protective layer of insulation, high vulnerability) and unaesthetic (round cables look better).
The ideal option is cables in which all signal lines are intertwined with common wires and enclosed in a common shield - which is required by IEEE 1248. These cables are guaranteed to operate at speeds up to 2 Mb / s with a length of up to 10 m.
Table 8.4 shows the wiring printer connection cable with connector X1 type A (DB25-P) on the PC side and X2 type B ( Centronics-36) or type C (miniature on the printer side. Using common wires ( GND) depends on the quality of the cable (see above). In the simplest case (18-wire cable), all GND signals are combined into one wire. High-quality cables require a separate return wire for each signal line, however, there are not enough contacts in the connectors of type A and B for this (in table 8.4, the numbers of contacts of the PC connector of type A are indicated in brackets, which correspond to the return wires). In type C connector, return wire ( GND) is available for each signal circuit; signal pins 1-17 of this connector correspond to pins GND 19-35.

Modern computers are highly capable of working with video, and their owners often watch films on the monitor screen. And with the advent of barebone multimedia platforms aimed at using as a home media center, interest in connecting audio and video equipment is only growing.
It is much more convenient and practical to watch video on a large TV screen, especially since almost all modern video cards are equipped with a TV output.
The need to connect a TV to a computer also arises when editing amateur video. As you can easily see in practice, the picture and sound on a computer are significantly different from those that you will later see and hear on TV. Therefore, all video editors allow you to view preliminary editing results on a television receiver directly from the working scale even before creating a movie. Experienced video enthusiasts constantly monitor the image and sound by displaying them on a television screen, not on a computer monitor.
Topics such as setting up video cards, choosing an image standard, as well as comparing the quality of video outputs of video cards from different manufacturers and solving the problems that arise are beyond the scope of this article - here we will consider only the following questions: what connectors can be found on a TV and on a video card, how they agree with each other and what are the ways to connect a computer to a TV.

Display interfaces

Classic analog interface (VGA)

Computers have been using the 15-pin analog D-Sub HD15 (Mini-D-Sub) interface, traditionally called the VGA interface, for quite some time. The VGA interface carries red, green, and blue (RGB) signals, as well as horizontal scan (H-Sync) and vertical sync (V-Sync) information.

All modern video cards have such an interface or provide it with an adapter from the universal combined DVI-I (DVI-integrated) interface.

Thus, both digital and analog monitors can be connected to the DVI-I connector. A DVI-I to VGA adapter is usually included with many graphics cards and allows you to connect older monitors with a 15-pin D-Sub (VGA) plug.

Please note that not every DVI interface supports analog VGA signals, which can be obtained through such adapters. Some video cards have a digital DVI-D interface to which you can connect only digital monitors. Visually, this interface differs from DVD-I by the absence of four holes (pins) around the horizontal slot (compare the right side of the white DVI connectors).

Often modern graphics cards are equipped with two DVI outputs, in which case they are usually universal - DVI-I. Such a video card can simultaneously work with any monitors, both analog and digital in any set.

DVI digital interface

The DVI interface (TDMS) was designed primarily for digital monitors that do not require the graphics card to convert digital signals to analog.

But because the transition from analog to digital displays is slow, graphics hardware designers typically use these technologies in parallel. In addition, modern video cards can work with two monitors simultaneously.

The universal DVI-I interface allows for both digital and analog connections, while DVI-D only digital. However, the DVI-D interface is quite rare today and is usually used only in cheap video adapters.

In addition, digital DVI connectors (both DVI-I and DVI-D) have two varieties - Single Link and Dual Link, which differ in the number of contacts (in Dual Link all 24 digital contacts are involved, and in Single Link - only 18 ). Single Link is suitable for use in devices with resolutions up to 1920x1080 (full HDTV resolution), for b abouthigher resolutions already require Dual Link, which allows you to double the number of displayed pixels.

HDMI digital interface

The digital multimedia interface HDMI (High Definition Multimedia Interface) was developed jointly by a number of large companies - Hitachi, Panasonic, Philips, Sony, etc. The 19-pin version of HDMI is widely used today to transmit high-definition television (HDTV) signals with a resolution of up to 1920x1080 (1080i ). Higher definition video requires 29-pin Type B connectors. In addition, HDMI can provide up to eight channels of 24-bit 192 kHz audio and has built-in Digital Rights Management (DRM) copyright protection.

HDMI is relatively new, but it has quite a few competitors in the computer sector, both from the traditional DVI interface and from newer and more advanced interfaces such as UDI or DisplayPort. However, products with HDMI ports are steadily moving into the market, as modern consumer video equipment is increasingly equipped with HDMI connectors. Thus, the growing popularity of multimedia computing platforms will stimulate the emergence of graphics and motherboards with HDMI ports, even though computer manufacturers have to buy a rather expensive license to use this standard and also pay some flat royalties for each product sold with an HDMI interface. ...

License fees also increase the cost of products with HDMI ports for the end manufacturer - for example, a video card with an HDMI port will cost about $ 10 more. In addition, it is unlikely that an expensive HDMI cable ($ 10-30) will be included in the package, so you will have to purchase it separately. However, there is hope that with the growing popularity of the HDMI interface, the size of such a markup will gradually decrease.

HDMI uses the same TDMS signal technology as DVI-D, so inexpensive adapters are available for these interfaces.

And while the HDMI interface has not yet replaced DVI, such adapters can be used to connect video equipment via the DVI interface. Please note that HDMI cables cannot be longer than 15m.

New UDI interface

At the beginning of this year, Intel announced a new digital interface UDI (Unified Display Interface) for connecting digital monitors to a computer. So far, Intel has just announced the development of a new type of connection, but in the near future it plans to completely abandon the old analog VGA interface and connect computers to display devices through a new digital interface UDI, recently developed by the engineers of this company.

The creation of the new interface is due to the fact that both the analog VGA interface and even the digital DVI interface, according to Intel representatives, are hopelessly outdated today. In addition, these interfaces do not support the latest content protection systems found in next generation digital media such as HD-DVD and Blu-ray.

Thus, UDI is practically analogous to the HDMI interface used to connect computers to modern HDTVs. The main (and perhaps the only) difference between UDI and HDMI will be the lack of an audio channel, that is, UDI will transmit only video and is entirely designed to work with computer monitors, not HD-TVs. In addition, Intel appears to be reluctant to pay licensing fees for every HDMI device it produces, so UDI is a good alternative for companies looking to reduce the cost of their products.

The new interface is fully compatible with HDMI, and will also support all currently known content protection systems, which will allow the smooth playback of new media equipped with copy protection.

New DisplayPort interface

Another new video interface, DisplayPort, was recently approved by the Video Electronics Standards Association (VESA) companies.

The open DisplayPort standard has been developed by a number of large companies, including ATI Technologies, Dell, Hewlett-Packard, nVidia, Royal Philips Electronics, and Samsung Electronics. It is assumed that in the future, DisplayPort will become a universal digital interface that allows you to connect displays of various types (plasma, liquid crystal, CRT monitors, etc.) to household devices and computer equipment.

DisplayPort 1.0 specification provides for the possibility of simultaneous transmission of both video signal and audio streaming (in this sense, the new interface is completely similar to HDMI). Note that the DisplayPort maximum throughput is 10.8 Gbps, with a relatively thin four-conductor interconnect cable used for transmission.

Another feature of DisplayPort is its support for content protection functions (similar to HDMI and UDI). Built-in security allows the content of a document or video to be displayed only on a limited number of “authorized” devices, which theoretically reduces the likelihood of illegal copying of copyrighted material. Finally, the new standard connectors are thinner than today's DVI and D-Sub connectors. This will allow DisplayPorts to be used in small form factor hardware and easily build multi-channel devices.

DisplayPort support has already been announced by Dell, HP and Lenovo. Most likely, the first devices equipped with new video interfaces will appear before the end of this year.

Video connector on graphics card

On modern video cards, in addition to connectors for connecting monitors (analog - D-Sub or digital - DVI), there is a composite video output ("tulip"), or a 4-pin S-Video output, or a 7-pin combined video output ( both S-Video and composite inputs and outputs).

In the case of S-Video, the situation is simple - there are S-Video cables or adapters for other SCART connectors on sale.

However, when a non-standard 7-pin connector is found on video cards, then in this case it is better to keep the adapter that comes with the video card, because there are several wiring standards for such a cable.

Composite video (RCA)

The so-called composite video output has long been widely used to connect consumer audio and video equipment. The connector for this signal is usually referred to as RCA (Radio Corporation of America), and popularly referred to as "tulip" or VHS connector. Please note that not only composite video or audio, but also many other signals such as component video or high definition television (HDTV) can be transmitted with such connectors in video equipment. Typically, tulip plugs are color coded to help users navigate the bundle of wires. Common meanings of colors are given in table. one.

Table 1

	Using	Signal type
White or black	Sound, left channel	Analog
	Sound, right channel	Analog
	Video, composite signal	Analog
	Luminance component signal (Luminance, Luma, Y)	Analog
	Chrominance, Chroma, Cb / Pb Component Signal	Analog
	Chrominance Component (Chrominance, Chroma, Cr / Pr)	Analog
Orange / yellow	SPDIF digital audio	Digital

Composite wires can be long enough (simple adapters can be used to extend wires).

However, the use of low quality connections and sloppy "tulip" switching is gradually becoming a thing of the past. In addition, cheap RCA connectors on equipment often break. Today, other types of switching are increasingly used on digital audio and video equipment, and even when transmitting analog signals, it is more convenient to use SCART.

S-Video

Often the video card and TV have a four-pin S-Video connector (Y / C, Hosiden), which is used to transmit video signals of higher quality than composite. The fact is that the S-Video standard uses different lines to transmit luminance (the luminance and data sync signal is denoted by the letter Y) and color (the chroma signal is denoted by the letter C). Separation of luminance and color signals allows to achieve better picture quality compared to the composite RCA interface ("tulip"). Higher quality analog video can only be achieved with completely separate RGB or component interfaces. To receive a composite signal from S-Video, a simple S-Video to RCA adapter is used.

If you do not have such an adapter, then you can make it yourself. However, there are two options for outputting a composite signal from a video card equipped with an S-Video interface, and the choice depends on the type of your video card. Some cards can switch output modes and send a simple composite signal to the S-Video output. In the mode of supplying such a signal to S-Video, you simply need to connect the pins to which the composite signal is supplied with the corresponding tulip outputs.

The RCA cable routing is simple: the video signal is fed through the center core, and the outer braid is the ground.

The S-Video layout is as follows:

• GND - "ground" for the Y-signal;
• GND - "ground" for the C-signal;
• Y - luminance signal;
• С - chrominance signal (contains both color difference).

If the S-Video-out can work in the composite signal supply mode, then the second pin of its connector is connected to ground, and the fourth - the signal. On a collapsible S-Video plug, which is required to make an adapter, the contacts are usually numbered. Jack and plug connectors are numbered mirrored.

If the video card does not have a composite signal output mode, then to obtain it, you will have to mix the chroma and luminance signal from the S-Video signal through a 470 pF capacitor. The signal received in this way is fed to the central core, and the “ground” from the second contact is fed to the braid of the composite cord.

SCART

SCART is the most interesting combined analog interface and is widely used in Europe and Asia. Its name comes from the French abbreviation proposed in 1983 by the Union of Developers of Radio and Television Equipment of France (Syndicat des Constructeurs d'Appareils, Radiorecepteurs et Televiseurs, SCART). This interface combines analog video (composite, S-Video, and RGB), stereo audio, and control signals. Today, every TV or VCR produced in Europe is equipped with at least one SCART socket.

For transmission of simple analog signals (composite and S-Video), there are many different SCART adapters on the market. This interface is convenient not only because everything is connected using only one cable, but also because it allows you to connect a high-quality RGB video source to a TV without intermediate encoding into composite or S-Video signals and get the best image quality on a consumer TV screen. (The picture and sound quality when fed through SCART is noticeably superior to that of any other analog connections). This possibility, however, is not realized in all VCRs and TVs.

In addition, the developers have incorporated additional capabilities into the SCART interface, having reserved several contacts for the future. And since the SCART interface became a standard in European countries, it has acquired several new features. For example, with the help of some signals on pin 8, you can control the TV modes via SCART (switch it to “monitor” mode and vice versa), switch the TV to work with RGB signals (pin 16), etc. Pins 10 and 12 are for digital data transmission via SCART, which makes the number of commands practically unlimited. There are several well-known SCART communication systems: Megalogic, used by Grundig; Easy Link from Philips; SmartLink from Sony. True, their use is limited to communication between the TV and VCR of these companies.

By the way, the standard provides for four types of SCART cables: type U - universal, providing all connections, V - without sound signals, C - without RGB signals, A - without video and RGB signals. Unfortunately, modern component modes (Y, Cb / Pb, Cr / Pr) are not supported in the SCART standard. However, some manufacturers of DVD-players and large-format TVs build in the ability to transmit via SCART and component video, which is transmitted through the pins used in the standard for the RGB signal (however, this feature is practically the same from connecting via RGB).

Various adapters are available for connecting composite or S-Video sources to SCART. Many of them are universal (bidirectional) with an I / O switch.

There are also simple unidirectional adapters, mono or stereo adapters, and connectors for switching control. In the case when it is necessary to connect two at once to one device, you can use a SCART splitter in two or three directions. Those who are not satisfied with the proposed options or who are not available can make their own in accordance with the pin assignments in SCART, given in Table. 2.

The pin numbering is usually indicated on the connector:

Of course, computers do not use a SCART connector, however, knowing its specification, you can always make an appropriate adapter for using an analog computer monitor as a receiver of a video signal from a tape recorder or, conversely, for supplying a video signal from a computer to a TV equipped with a SCART connector.

For example, in order to input or output a composite signal from a SCART connector, you need to take a coaxial cable with a characteristic impedance of 75 ohms and distribute the outer braid (ground) and the inner core (composite signal) on the SCART connector.

Video signal output from computer to TV (TV-OUT):

• the composite signal is fed to pin 20 of the SCART connector;

To input the video signal from the VCR to the computer (TV-IN):

• composite signal - to the 19th pin of the SCART connector;
• "Ground" - to the 17th pin of the SCART connector.

The correspondence of contacts in the manufacture of an adapter for S-Video is also indicated in table. 2.

Video signal output from computer to TV via S-Video (TV-OUT):

• 3rd S-Video pin - 20th SCART pin;

Video signal input from a VCR to a computer via S-Video (TV-IN):

• 1st S-Video pin - 17th SCART pin;
• 2nd S-Video pin - 13th SCART pin;
• 3rd S-Video pin - 19th SCART pin;
• 4th S-Video pin - 15th SCART pin.

To connect a computer to a TV using RGB, it is necessary for the computer to output an RGB signal in a form that the TV can understand. Sometimes the RGB signal is fed through a dedicated 7-, 8-, or 9-pin composite video output. In this case, the video card settings should be able to switch the video output to RGB mode. If the video output on a video card has seven pins (such a plug is called a mini-DIN 7-pin), then in normal mode the S-Video signal is fed exactly to the same pins as in a regular four-pin S-Video connector. And in RGB mode, signals can be distributed to contacts in different ways, depending on the manufacturer of the video card.

As an example, we can give the correspondence of the contacts of one of these 7-pin connectors with SCART (this wiring is used on some video cards based on the NVIDIA chip, but it may be different on your video card):

• 1st mini-DIN 7-pin contact (GND, "ground") - 17th SCART contact;
• 2nd pin mini-DIN 7-pin (Green, green) - 11th pin SCART;
• 3rd pin mini-DIN 7-pin (Sync, sweep) - 20th pin SCART;
• 4th pin mini-DIN 7-pin (Blue) - 7th pin SCART;
• 5th pin mini-DIN 7-pin (GND, "ground") - 17th pin SCART;
• 6th pin mini-DIN 7-pin (Red, red) - 15th pin SCART;
• 7th pin mini-DIN 7-pin (+3 V RGB mode control) - 16th pin SCART.

All types of adapters require the use of high quality 75 Ohm cables.

There is no video connector on the graphics card

If your video card does not have a TV output, then, in principle, a TV can be connected to a regular VGA connector. However, in this case, an electrical signal matching circuit will be required (in the general case, however, it is not complicated). There are special devices on the market that convert regular computer VGA signals to RGB and a scan (sync) signal for the TV. Such a device connects to the VGA cable between the computer and the monitor and duplicates the signal that goes through the VGA output.

In principle, such a device can be made independently. The correspondence between VGA and SCART signals will be as follows:

• VGA SCART PIN SCART Description;
• VGA RED - to the 15th SCART pin;
• VGA GREEN - to the 11th SCART pin;
• VGA BLUE - to the 7th SCART pin;
• VGA RGB GROUND - on the 13th, or 9th, or 5th SCART pin;
• VGA HSYNC & VSYNC - on the 16th and 20th SCART pins.

You will also need to apply + 1-3 V to the 16th SCART pin and 12V to the 8th SCART pin to switch to AV mode with an aspect ratio of 4: 3.

However, a direct connection will most likely not work and for synchronization you will have to make an electrical circuit, as shown at http://www.tkk.fi/Misc/Electronics/circuits/vga2tv/circuit.html or http: //www.e.kth .se / ~ pontusf / index2.html.

Lecture 6. Interfaces and display adapters

Display interfaces.

Display adapters.

Video system parameters.

Literature: 1. Guk. M. Hardware IBM PC. Peter, 2005, p. 510-545.

1. Display interfaces.

1.1. General characteristics of display interfaces.

In the traditional technology of color television broadcasting (PAL, SECAM or NTSC), the video signal directly carries information about the instantaneous value of the brightness f n, and the color information is transmitted in modulated form at additional frequencies f d. This ensures the compatibility of a black-and-white receiver that ignores color information. with a color transmission channel.

f d1 \u003d 4.43 MHz f n \u003d 4.5 MHz f d2 \u003d 4.6 MHz

However, none of the traditional broadcast systems is suitable for displaying high-resolution graphics information, since they have a significantly limited bandwidth of color channels (i.e., the minimum 35 MHz is unattainable). For monitors at high resolution, only direct signal feed to the inputs of video amplifiers of basic colors can be used - RGB-entrance (Red Green Blue - red, green and blue).

The interface between the video adapter and the monitor can be either discrete (with TTL signals) or analog. Evolutionary discrete interface for monochrome and early color monitors CGA and EGA replaced by the now popular analog interface VGA, providing the transfer of a large number of colors. However, further the quality of the analog signal transmission ceased to meet the growing needs (with an increase in the scanning frequency and resolution), and a new digital interface appeared. DVI... For flat panel displays with their matrix organization and relatively high inertia of cells, it is advisable to use a specialized digital interface (Flat Panel Monitor Interface, but not DVI).

In modern adapters, it is again possible to connect a standard TV through a special signal converter. For the television interface, it is possible to provide synchronization from an external television system (converter), which is important for combining a computer video signal with an external "television environment".

1.2. Discrete rgb ttl interface

The first PC monitors had a discrete interface with TTL levels. RGB TTL. For a monochrome monitor, only two signals were used - video (turn on / off the beam) and high brightness. Thus, the monitor could display three grades of brightness: although 2 2 - 4, "dark pixel" and "dark with increased brightness" are indistinguishable.

On / Off Monitor

In color monitors of the class CD { Color Display) there was one signal to turn on each beam and a general signal of increased brightness. Thus, 4 2 \u003d 16 colors could be set.

G Monitor

The next class is the improved color display ECD (Enhanced Color Display) had a discrete interface with two signals for each base color. The signals made it possible to set one of four intensity gradations; the total number of coded colors has reached (2 2) 3 \u003d 2 6 \u003d 64.

2 - two signals per channel;

3 - three channels.

Signals RED, GREEN, BLUE and Red, Green, Blue denote the most significant and least significant bits of the base colors, respectively.

G, g Monitor

H.Sync and V.Sync signals are used for horizontal and vertical synchronization of the monitor. (Horizontal, Vertical sync)