Сандық тіркегіштер және олардың түрлері

Device storing number of times an event or process occurred
the term counter used in electronics, computing, and mechanical counting devices

In digital logic and computing, 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. The most common type is a sequential digital logic circuit with an input line called the clock and multiple output lines. The values on the output lines represent a number in the binary or BCD number system. Each pulse applied to the clock input increments or decrements the number in the counter. A counter circuit is usually constructed of several flip flops connected in a cascade. Counters are a very widely used component in digital circuits, and are manufactured as separate integrated circuits and also incorporated as parts of larger integrated circuits.

In a synchronous counter, the clock inputs of the flip flops are connected, and the common clock simultaneously triggers all flip flops. Consequently, all of the flip flops change state at the same time (in parallel). For example, the circuit shown to the right is an ascending (up counting) four bit synchronous counter implemented with JK flip flops. Each bit of this counter is allowed to toggle when all of the less significant bits are at a logic high state. Upon clock rising edge, bit 1 toggles if bit 0 is logic high; bit 2 toggles if bits 0 and 1 are both high; bit 3 toggles if bits 2, 1, and 0 are all high.

A decade counter counts in decimal digits, rather than binary. A decade counter may have each (that is, it may count in binary coded decimal, as the 7490 integrated circuit did) or other binary encodings. A decade counter is a binary counter designed to count to 1001 (decimal 9). An ordinary four stage counter can be easily modified to a decade counter by adding a NAND gate as in the schematic to the right. Notice that FF2 and FF4 provide the inputs to the NAND gate. The NAND gate outputs are connected to the CLR input of each of the FFs.". It counts from 0 to 9 and then resets to zero. The counter output can be set to zero by pulsing the reset line low. The count then increments on each clock pulse until it reaches 1001 (decimal 9). When it increments to 1010 (decimal 10), both inputs of the NAND gate go high. The result is that the NAND output goes low, and resets the counter to zero. D going low can be a CARRY OUT signal, indicating that there has been a count of ten.

A ring counter is a circular shift register that is initiated such that only one of its flip flops is the state one while others are in their zero states. A ring counter is a shift register (a cascade connection of flip flops) with the output of the last one connected to the input of the first, that is, in a ring. Typically, a pattern consisting of a single bit is circulated, so the state repeats every n clock cycles if n flip flops are used.

A Johnson counter (or switch tail ring counter, twisted ring counter, walking ring counter, or Möbius counter) is a modified ring counter, where the output from the last stage is inverted and fed back as input to the first stage. The register cycles through a sequence of bit patterns, whose length is equal to twice the length of the shift register, continuing indefinitely. These counters find specialist applications similar to the decade counter (note: the 74x4017 decade counter is a Johnson counter), digital to analog conversion, etc. They can be implemented easily using D or JK type flip flops.

A web counter or hit counter is a computer program that indicates the number of visitors or hits a particular webpage has received. Once set up, these counters will be incremented by one every time the web page is accessed in a web browser. The number is usually displayed as an inline digital image or in plain text or on a physical counter such as a mechanical counter. Images may be presented in a variety of fonts, or styles; the classic example is the wheels of an odometer. Web counter was popular in the mid to late 1990s and early 2000s, later replaced by more detailed and complete web traffic measures.

Many automation systems use PC and laptops to monitor different parameters of machines and production data. Counters may count parameters such as the number of pieces produced, the production batch number, and measurements of the amounts of material used.

Long before electronics became common, mechanical devices were used to count events. These are known as tally counters. They typically consist of a series of disks mounted on an axle, with the digits zero through nine marked on their edge. The right most disk moves one increment with each event. Each disk except the left most has a protrusion that moves the next disk to the left one increment after the completion of one revolution. Such counters were used as odometers for bicycles and cars and in tape recorders, fuel dispensers, in production machinery as well as in other machinery. One of the largest manufacturers was the Veeder Root company, and their name was often used for this type of counter. Handheld tally counters are used mainly for stocktaking and counting people attending events. Electromechanical counters were used to accumulate totals in tabulating machines that pioneered the data processing industry.