Polling (often called scanning in this case) is done by activating each x line in sequence and detecting which y lines then have a signal, thus which keys are pressed. When a switch is pressed, it connects the corresponding x and y lines together. But it does not scale to support more keys than the number of bits in a single byte or word.ĭevices with many switches (such as a computer keyboard) usually arrange these switches in a scan matrix, with the individual switches on the intersections of x and y lines. This is useful when combinations of key presses are meaningful, and is sometimes used for passing the status of modifier keys on a keyboard (such as shift and control). When a new symbol has been entered, the device typically sends an interrupt, in a specialized format, so that the CPU can read it.įor devices with only a few switches (such as the buttons on a joystick), the status of each can be encoded as bits (usually 0 for released and 1 for pressed) in a single word. This polling can be done by a specialized processor in the device to prevent burdening the main CPU. Data will be lost if, within a single polling interval, two switches are pressed, or a switch is pressed, released, and pressed again. Instead of sampling and quantization as in analog-to-digital conversion, such techniques as polling and encoding are used.Ī symbol input device usually consists of a group of switches that are polled at regular intervals to see which switches are switched.
Since symbols (for example, alphanumeric characters) are not continuous, representing symbols digitally is rather simpler than conversion of continuous or analog information to digital. ( August 2016) ( Learn how and when to remove this template message) Statements consisting only of original research should be removed. Please improve it by verifying the claims made and adding inline citations. This section possibly contains original research.
The term is most commonly used in computing and electronics, especially where real-world information is converted to binary numeric form as in digital audio and digital photography. Mathematician George Stibitz of Bell Telephone Laboratories used the word digital in reference to the fast electric pulses emitted by a device designed to aim and fire anti-aircraft guns in 1942. The word digital comes from the same source as the words digit and digitus (the Latin word for finger), as fingers are often used for counting.
An example is the air pressure variation in a sound wave. Analog data is transmitted by an analog signal, which not only takes on continuous values, but can vary continuously with time, a continuous real-valued function of time. The most common form of digital data in modern information systems is binary data, which is represented by a string of binary digits (bits) each of which can have one of two values, either 0 or 1.ĭigital data can be contrasted with analog data, which is represented by a value from a continuous range of real numbers. An example is a text document, which consists of a string of alphanumeric characters. The actual precise time is analog data.ĭigital data, in information theory and information systems, is information represented as a string of discrete symbols each of which can take on one of only a finite number of values from some alphabet, such as letters or digits. The time shown by the digits on the face at any instant is digital data.