Trigger

Trigger is an element of digital technology designed to generate an information signal at the output in accordance with some simplest function. Depending on the function, triggers are divided into a number of types.

The meanings of the word trigger

Before plunging into the wilds of digital technology, we note: the term trigger is used in various industries as a trigger for a switch mechanism. Gamers call the word a trigger, programmers - a test script that helps to assess the presence of an object in virtual reality.

For gamers, we note that the game Dead Trigger 2( a continuation of the shooter of the same name) is unsuccessful, if it was not intended entirely for the owners of mobile devices. The operating system is Android. Imagine a primitive blend of Quake and Counter Strike to understand poorly what the main character will have to face. On a size-limited map, a bunch of zombies roam the hero must kill. Hitting the head will significantly speed up the process, although not individually fixed. Poured Counter Strike.

Clearly, the term trigger for gamers sounds depressing. Maximum - an option to kill time.

The trigger of digital equipment

. Under the trigger digital technology understand the simplest machine with two states. The transition between them is determined by the function according to which the species are distinguished( RS, D, T, JK).In the schemes, the trigger is often depicted as a rectangular frame-body, equipped with several entrances, a pair of outputs( the type of side legs), the letter from the above is put. Sometimes the device is synchronous. Then the letter C is added to the inputs, catching the clock pulses. Other asynchronous triggers.

Depending on the implemented function, there are types of devices:

1. RS are intended to control the output with the help of two inputs. The first will serve the purpose of setting the unit, translated Set. The trigger is set to the zero state by activating the R input( Reset).
2. D( data, delay) trigger remembers the value of its own input, acts as a delay device. If the device variant is synchronous, the value is transmitted to the output in the next clock cycle.
3. T( toggle) trigger knows how to count in the binary system. The output alternately becomes 0-1 with the arrival of each unit at the counting input. Sometimes called frequency divider( 2).

It seems surprising that it is possible to assemble complex conglomerates on the basis of a poor set of functions. In nature, there are JK-triggers, called universal. Due to the specific construction, logical units can be fed to both inputs, which are unable to survive RS-flip-flops. JK-trigger implements the concept of the counter. In other situations, the behavior is similar to RS.Let's take a closer look at the elements of digital technology.

A common feature of

triggers. History of the creation of

. The first trigger was proposed in 1918 by William Eccles, Frank Jordan. Composed of two vacuum tubes, the design was used by the technique, including the British computer Colossus( 1943).Then the technical solution smoothly migrated to semiconductor technology, often called multivibrators for specific behavior.

According to the research of researchers, in its current form, the D, T, RS, and JK triggers were discussed for the first time in 1954, limited to the Montgomery Fister course of study courses at the University of Los Angeles, then referred to as a book by a scholar, involving computer design. The titles are invented by the lecturer, excluding JK.The latter is taken from the works of Eldred Nelson, who gives triggers names in his own texts, borrowing in pairs from the Latin alphabet: AB, C-D.One was called JK.Fister, avoiding changes, took over the name.

Asynchronous triggers are often referred to as snaps, it gets started in the context of memory devices. Others - clocked. An arbitrary trigger can be built on a pair of switches, including transistors.

Outputs and States

Each trigger is equipped with two outputs, one indicated by the overlined letter Q, a circle in the foot area, is inverse. If the main output is 1, there will be zero here. Understandably from the context, there are two trigger states. Inverse considered inputs. The logic is reversed. The unit at the S input causes the output to be set to zero.

The composition of the trigger

Each trigger is represented by the simplest elements formed by an arbitrary basic chipset logic. CMOS, TTL, TTLSH, ECL.The composition of each contains a basis, AND-NOT elements( denoted by the symbol &), OR-NOT( denoted by 1).It is possible to build the necessary triggers from the bricks. Much more often the structure is replenished with ready technical solutions. For example, K555TP2, represents 4 RS-flip-flops, united by one body.

Before fencing the garden, work to get a good guide to the chips to see what is invented at the moment. We add that the series differ among themselves by logical levels, synchronization frequency, and some other parameters. Technological properties laid the name:

• TTL - transistor-transistor logic.
• ECL - emitter-coupled logic.
• CMOS is a derivative of the English abbreviation CMOS( complementary metal oxide semiconductor).

Fictionalized many options, ways to build digital technology, most of the Russian series of microcircuits have known non-existence. However, today we read: the next central processor of Intel or AMD includes such a number of transistors. Triggers, other elements inside the electronic brain are available. Deprived of the simplest bricks of digital technology is not feasible.

So, the trigger is free to represent in the form of basic functions( chips) AND-NOT, OR-NOT and others. Why is that? The subject of discrete mathematics proves: an arbitrarily complex function is realizable by a combination of the simple ones mentioned. Created methods of analysis, synthesis. A trigger is an operation of this kind, a logical action.

A set of basic functions is implemented through the circuitry of transistor gates. In some cases it is convenient to use TTL, in others - ECL.Synchronization is introduced for orderliness. Without clock pulses, the result of the operation of the elements, including triggers, depended on the speed of the elementary components of the transistors. Since the number of trigger bricks is unique, speed cannot be predicted in advance. The task is too complicated.

Another way to say: triggers are considered functions that are most often used by technology. In order to stop reinventing the wheel, ready-made microcircuits are produced that can perform a fixed operation. It is considered that each series of microcircuits must become self-sufficient and convenient. Each function of digital technology is possible to implement with two elements, it does not always look rational from the point of view of the time spent. In order for the printed circuit boards to come out not so bulky, the plant conveyor assembles the common functions.

It should be understood that the division of triggers is considered conditional, established, considered the most convenient for designers of digital equipment. Nature has given birth a little: RS, D, T, JK.

RS-trigger

Trigger with input control. By applying a logical unit to the S-input, the output Q is set to one. With R, on the contrary, a zero output state is obtained. It is forbidden to give units to both inputs, the result is unpredictable: you cannot know in advance what the outcome will be. Circuit RS-flip-flop can consist of two identical transistors, several passive elements.

elements The figure shows an example of constructing an RS-trigger by OR-NOT and AND-NO elements. You see, in the second case, the inputs turned out to be inverse, marked with circles. Easy to check, the table of values ​​has been inverted. For setting Q into one, the input R is responsible. The logical units of both inputs ensure the preservation of information. The trigger captures the state.

D-trigger

Although the D-trigger is usually built directly on the 4 elements of the basic logic, it works much easier. Information input D is transmitted to the output. In the case of a synchronous version occurs on the next clock. As mentioned above, allows you to easily organize a delay line.

Highlight D-triggers with dynamic, potential control. In the first case, the entry of indications at the exit is made on the front of the clock pulse, in the second - at the top. The dynamic inputs of the circuits are marked with triangles, allowing the developer to build correctly, the engineer to understand the principle of operation. And the triangle can be directed in different directions:

• A vertex facing the microchip means: information is read on the leading edge of a clock pulse.
• A vertex, facing away from the microchip, means: information is read on the falling edge( slice) of the clock pulse. The value will surely be delayed by one cycle compared to the previous version.

Very often triggers are characterized by an internal delay. The time after which the output sets the desired value relative to the working front( decay).One of the characteristics that shows why different types of logic does not work together. The parameter applies to all types of triggers, not just D.

T-flip-flop

T-flip-flop counts the impulses arriving at the information input without any problems. Usually the design is synchronous. Otherwise, it is difficult to predict the result: at a certain frequency of input pulses, the device will not have time to switch. Technique will produce failures. The T-flip-flop is often used as a divider, from two input pulses it allows to get one output.

T-trigger in the finished form in the chip series is usually not included. Instead, the device is created on the basis of a D-flip-flop( you need to close the inverse output to the information input) or JK.To create multi-bit counters, T-triggers are connected in series one after another. Simple methods are used to dividers by 4, 8 and other powers of two.

JK-flip-flop

JK-flip-flop works like a RS.J becomes the unit setup input Q output;K - zero. If two units are submitted at once, the element implements the counting mode. Usually there is a synchronization input, according to the signal on which samples are taken. JK is the only type of trigger, the letter designation of the inputs of which is devoid of logical sense. Borrowed from the works of the scientist who built the basic elements of the Latin alphabet.