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Encyclopedia > Counter

In general, a counter is a device which stores (and sometimes displays) the number of times a particular event or process has occurred, often in relationship to a clock signal. In practice, there are two types of counters: This page is a candidate for speedy deletion because: this page is a test If you disagree with its speedy deletion, please explain why on its talk page or at Wikipedia:Speedy deletions. ... Process (lat. ... In synchronous digital electronics, such as most computers, a clock signal is a signal used to coordinate the actions of two or more circuits. ...

  • up counters which increase (increment) in value
  • down counters which decrease (decrement) in value

Contents

An increment is an increase, either of some fixed amount, for example added regularly, or of a variable amount. ... An increment is an increase, either of some fixed amount, for example added regularly, or of a variable amount. ...

Counters in electronics

Toggle flip-flop. Output is not shown. Red=1, blue=0
Toggle flip-flop. Output is not shown. Red=1, blue=0

In electronics, counters can be implemented quite easily using register-type circuits such as the flip-flop, and a wide variety of designs exist, e.g: Image File history File links T_flip-flop. ... // Electronics is the study of electron mechanics. ... In digital circuits, the flip-flop, latch, or bistable multivibrator is an electronic circuit which has two stable states and thereby is capable of serving as one bit of memory. ...

  • Asynchronous (ripple) counters
  • Synchronous counters
  • Johnson counters
  • Decade counters
  • Up-Down counters
  • Ring counters

Each is useful for different applications. Usually, counter circuits are digital in nature, and count in binary, or sometimes binary coded decimal. Many types of counter circuit are available as digital building blocks, for example a number of chips in the 4000 series implement different counters. A digital system is one that uses discrete values (often electrical voltages), especially those representable as binary numbers, or non-numeric symbols such as letters or icons, for input, processing, transmission, storage, or display, rather than a continuous spectrum of values (ie, as in an analog system). ... The term binary code can mean several different things: There are a variety of different methods of coding numbers or symbols into strings of bits, including fixed-length binary numbers, prefix codes such as Huffman code, and other arithmetic coding. ... Binary-coded decimal (BCD) is a numeral system used in computing and in electronics systems. ... The 4000 series is the general classification used to refer to the industry standard integrated circuits which implement a variety of logic functions using CMOS technology. ...


Asynchronous (ripple) counters

Asynchronous Counter created from JK flip-flops.
Asynchronous Counter created from JK flip-flops.

The simplest counter circuit is a single D-type flip flop, with its D (data) input fed from its own inverted output. This circuit can store one bit, and hence can count from zero to one before it overflows (starts over from 0). This counter will increment once for every clock cycle and takes two clock cycles to overflow, so every cycle it will alternate between a transition from 0 to 1 and a transition from 1 to 0. Notice that this creates a new clock with a 50% duty cycle at exactly half the frequency of the input clock. If this output is then used as the clock signal for a similarly arranged D flip flop (remembering to invert the output to the input), you will get another 1 bit counter that counts half as fast. Putting them together yields a two bit counter: Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... In digital circuits, the flip-flop, latch, or bistable multivibrator is an electronic circuit which has two stable states and thereby is capable of serving as one bit of memory. ... In telecommunication and electronics, the term duty cycle has the following meanings: The duty cycle D is defined as the ratio between the pulse duration () and the period (T) of a rectangular waveform In a periodic phenomenon, the ratio of the duration of the phenomenon in a given period to...

cycle Q1 Q0 (Q1:Q0)dec
0 0 0 0
1 0 1 1
2 1 0 2
3 1 1 3
4 0 0 0

You can continue to add additional flip flops, always inverting the output to its own input, and using the output from the previous flip flop as the clock signal. The result is called a ripple counter, which can count to 2n-1 where n is the number of bits (flip flop stages) in the counter. Ripple counters suffer from unstable outputs as the overflows "ripple" from stage to stage, but they do find frequent application as dividers for clock signals, where the instantaneous count is unimportant, but the division ratio overall is. (To clarify this, a 1-bit counter is exactly equivalent to a divide by two circuit - the output frequency is exactly half that of the input when fed with a regular train of clock pulses). A ratio is a quantity that denotes the proportional amount or magnitude of one quantity relative to another. ...


Synchronous counters

A 4-bit synchronous counter
A 4-bit synchronous counter

Where a stable count value is important across several bits, which is the case in most counter systems, synchronous counters are used. These also use flip-flops, either the D-type or the more complex J-K type, but here, each stage is clocked simultaneously by a common clock signal. Logic gates between each stage of the circuit control data flow from stage to stage so that the desired count behaviour is realised. Synchronous counters can be designed to count up or down, or both according to a direction input, and may be presettable via a set of parallel "jam" inputs. Most types of hardware-based counter are of this type. Download high resolution version (1712x943, 21 KB) Wikipedia does not have an article with this exact name. ... Download high resolution version (1712x943, 21 KB) Wikipedia does not have an article with this exact name. ... A logic gate performs a logical operation on one or more logic inputs and produces a single logic output. ...

Johnson counters

A Johnson counter is a special case of shift register, where the output from the last stage is inverted and fed back as input to the first stage. A pattern of bits equal in length to the shift register thus circulates indefinitely. These counters are sometimes called "walking ring" counters, and find specialist applications, including those similar to the decade counter, digital to analogue conversion, etc. In digital circuits a shift register is a group of registers set up in a linear fashion which have their inputs and outputs connected together in such a way that the data is shifted down the line when the circuit is activated. ...


Decade counters

Decade counters are a kind of counter that counts in tens rather than having a binary representation. Each output will go high in turn, starting over after ten outputs have occurred. This type of circuit finds applications in multiplexers and demultiplexers, or wherever a scanning type of behaviour is useful. Similar counters with different numbers of outputs are also common. Schematic of a 2-to-1 Multiplexer. ...


Up-Down Counters

It is a combination of up counter and down counter, counting in straight binary sequence. There is an up-down selector. If this value is kept high, counter increments binary value and if the value is low, then counter starts decrementing the count. Template:Sectsub


Ring Counters

Instead of counting with binary numbers, a ring counter counts with words that have a single high bit. These are ideal for timing a sequence of digital operations.


See also: Frequency counter A frequency counter is an electronic instrument, or component of one, that is used for measuring frequency. ...


Counters in computer science

Main article: Register machine

In computability theory, a counter is considered a type of memory. A counter stores a single natural number (initially zero) and can be arbitrarily many digits long. A counter is usually considered in conjunction with a finite state machine (FSM), which can perform the following operations on the counter: In theoretical computer science a register machine is an abstract machine used to study decision problems, similar to how a Turing machine is used. ... In computer science, computability theory is the branch of the theory of computation that studies which problems are computationally solvable using different models of computation. ... In mathematics, a natural number can mean either an element of the set {1, 2, 3, ...} (i. ... 0 (zero) is both a number and a numerical digit used to represent that number in numerals. ... Fig. ...

  • Check whether the counter is zero
  • Increment the counter by one
  • Decrement the counter by one (if it's already zero, this leaves it unchanged).


The following machines are listed in order of power, with each one being strictly more powerful than the one below it:

  1. Deterministic or Non-deterministic FSM plus two counters
  2. Non-deterministic FSM plus one stack
  3. Non-deterministic FSM plus one counter
  4. Deterministic FSM plus one counter
  5. Deterministic or Non-deterministic FSM

For the first and last, it doesn't matter whether the FSM is deterministic or non-deterministic (see determinism). They have equivalent power. The first two and the last one are levels of the Chomsky hierarchy. Simple representation of a stack In computer science, a stack is a temporary abstract data type and data structure based on the principle of Last In First Out (LIFO). ... In the theory of computation, a deterministic finite state machine or deterministic finite automaton (DFA) is a finite state machine where for each pair of state and input symbol there is one and only one transition to a next state. ... The Chomsky hierarchy is a containment hierarchy of classes of formal grammars that generate formal languages. ...


The first machine, an FSM plus two counters, is equivalent in power to a Turing machine. See the article on register machines for a proof. An artistic representation of a Turing Machine . ... In theoretical computer science a register machine is an abstract machine used to study decision problems, similar to how a Turing machine is used. ...


See also


  Results from FactBites:
 
BoingDragon's Lair | Counters (5484 words)
The main problem with the counter logging right now is that it isn't resolving IP addresses, which kills the 'top 20 visitor domains' part of the reporting (the older counters had this, and I'm trying to maintain all of the same reporting features).
Some of the old counters will no longer be available in their current form, as I'm switching most of the 'overlay' ones (fairy, unicorn, etc) back to optimized inline images.
The counters are going to be limited to 2000 hits/day at first, so it really counts as a beta test for how much the system can handle.
WWW Homepage Access Counter and Clock (9310 words)
The implication is, if the counter is the first thing in a large table, the browser will not have to wait to calculate the width and height of the counter image before loading the rest.
The parameter offset is used with parameter align to specify the offset of the counter image in pixels from the edge of the base image while compositing the counter/clock image with an base image.
You can position the counter image anywhere on the base image using the parameter xy or you can use align to align at top, middle and bottom of the base image.
  More results at FactBites »

 
 

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