Civil Rights
Movements, leaders, victories and the continuing fight for equality.
q2K BHP
Black History Portal
THE BHP WIRE —
HIDDEN TRUTHS
What's New!
Explore the people, places, events, achievements, struggles and stories that shaped our journey.
Movements, leaders, victories and the continuing fight for equality.
Innovation, patents, science, technology and world-changing contributions.
Pioneers, champions, Negro Leagues, records, activism and excellence.
Meet the people whose lives, choices and achievements shaped the journey.
Black towns, communities, institutions and places where history happened.
Moments that changed communities, movements, institutions and the nation.
Mansa Musa was the ruler of the Mali Empire in West Africa. Details recorded here should be sourced; unknown information is left blank.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
 | This article needs more citations. (September 2014) |
Multiplexed displays are electronic display devices where the entire display is not driven at one time.
Instead, sub-units of the display (typically, rows or columns for a dot matrix display or individual characters for a character oriented display, occasionally individual display elements) are multiplexed, that is, driven one at a time, but the high switching frequency and the persistence of vision combine to make the viewer believe the entire display is continuously active.
A multiplexed display has several advantages compared to a non-multiplexed display:
Multiplexed displays can be divided into two broad categories:
Most character-oriented displays (such as seven-segment displays, fourteen-segment displays, and sixteen-segment displays) display an entire character at one time. The various segments of each character are connected in a two-dimensional diode matrix and will only illuminate if both the "row" and "column" lines of the matrix are at the correct electrical potential. The light-emitting element normally takes the form of a light-emitting diode (LED) so electricity will only flow in one direction, keeping the individual "row" and "column" lines of the matrix electrically isolated from each other. For liquid crystal displays, the intersection of the row and column is not conductive at all.
In the example of the VCR display shown above, the illuminated elements are the plates of many individual triode vacuum tubes sharing the same vacuum enclosure. The grids of the triodes are arranged so that only one digit is illuminated at a time. All of the similar plates in all of the digits (for example, all of the lower-left plates in all of the digits) are connected in parallel. One by one, the microprocessor driving the display enables a digit by placing a positive voltage on that digit's grid and then placing a positive voltage on the appropriate plates. Electrons flow through that digit's grid and strike those plates that are at a positive potential.
If the display had been built with every segment being individually connected, the display would have required 49 wires just for the digits, with more wires being needed for all of the other indicators that can be illuminated. By multiplexing the display, only seven "digit selector" lines and seven "segment selector" lines are needed. The extra indicators (in our example, "VCR", "Hi-Fi", "STEREO", "SAP", etc.) are arranged as if they were segments of an additional digit or two or extra segments of existing digits and are scanned using the same multiplexed strategy as the real digits.
Most character-oriented displays drive all the appropriate segments of an entire digit simultaneously. A few character-oriented displays drive only one segment at a time. The display on the Hewlett-Packard HP-35 was an example of this. The calculator took advantage of an effect of pulsed LED operation where very brief pulses of light are perceived as brighter than a longer pulse of light with the same time-integral of intensity.
A keyboard matrix circuit has a very similar arrangement as a multiplexed display, and has many of the same advantages. In order to reduce the number of wires even further, some people "share" wires between a multiplexed display and a keyboard matrix, reducing the number of wires even further.[1]
By comparison, in dot-matrix displays, individual pixels are located at the intersections of the matrix's "row" and "column" lines and each pixel can be individually controlled.
Here, the savings in wiring becomes far more dramatic. For a typical 1024×768 (XGA) computer screen, 2,359,297 wires would be needed for non-multiplexed control. That many wires would be completely impractical. But by arranging the pixels into a multiplexed matrix, only 3,328 wires are needed; a more practical situation.
Pixel-oriented displays may drive a single pixel at a time or an entire row or column of pixels simultaneously. Active-matrix liquid crystal displays provide a storage element at each pixel so that the pixel continues to display the correct state even when not being actively driven.
Because most multiplexed displays do not present the entire display simultaneously, they are subject to "break up" if the observer's point of regard is in motion. For example, if the observer were to rapidly swing their vision across a multiplexed display, they might see a jumble of individual digits rather than a coherent display. (The same effect can occur if the display is moving with respect to the observer's point of regard.) People with nystagmus (involuntary eye movement) are much more likely to experience the effect and may find some multiplexed displays hard to read. It can also sometimes be provoked by chewing hard candy; this causes vibration of the user's eyes, leading to the break-up of the display.
The multiplexed nature of a display can also be revealed by observing it through a mechanical stroboscope, for example, a spinning slotted wheel.
Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
Multiplexed displays are electronic display devices where the entire display is not driven at one time. Instead, sub-units of the display (typically, rows or columns for a dot matrix display or individual characters for a character oriented display, occasionally individual display elements) are multiplexed, that is, driven one at a time, but the high switching frequency and the persistence of vision combine to make the viewer believe the entire display is continuously active. A multiplexed display has several advantages compared to a non-multiplexed display: fewer wires (often, far fewer wires) are needed simpler driving electronics can be used both lead to reduced cost reduced power consumption Multiplexed displays can be divided into two broad categories: character-oriented displays pixel-oriented displays
In telecommunications and computer networking, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a transmission medium. It allows the same medium to be shared between multiple users. The aim is to share a scarce resource—a physical transmission medium. For example, in telecommunications, several telephone calls may be carried using one wire. Multiplexing originated in telegraphy in the 1870s, and is now widely applied in communications. In telephony, George Owen Squier is credited with the development of telephone carrier multiplexing in 1910. The multiplexed signal is transmitted over a communication channel such as a cable. The multiplexing divides the capacity of the communication channel into several logical channels, one for each message signal or data stream to be transferred. A reverse process, known as demultiplexing, extracts the original channels on the receiver end. A device that performs the multiplexing is called a multiplexer (MUX), and a device that performs the reverse process is called a demultiplexer (DEMUX or DMX). Inverse multiplexing (IMUX) has the opposite aim as multiplexing, namely to break one data stream into several streams, transfer them simultaneously over several communication channels, and recreate the original data stream. In computing, I/O multiplexing can also be used to refer to the concept of processing multiple input/output events from a single event loop, with system calls like poll and select (Unix).
A multiplex or mux, also known as a bouquet, is a grouping of program services as interleaved data packets for broadcast over a network or modulated multiplexed medium, particularly terrestrial broadcasting. The program services are broadcast as part of one transmission and split out at the receiving end. The conversion from analog to digital television made it possible to transmit more than one video service, in addition to audio and data, within a fixed space previously used to transmit one analog TV service (varying between six and eight megahertz depending on the system used and bandplan). The capacity of a multiplex depends on several factors, including the video resolution and broadcast quality, compression method, bitrate permitted by the transmission standard, and allocated bandwidth; statistical time-division multiplexing is often used to dynamically allocate bandwidth in accordance with the needs of each individual service. Each service in a multiplex has a separate virtual channel (also known as a logical channel number) for identification and tuning. Depending on the country, a multiplex may be controlled by one broadcaster offering multiple subchannels or may feature services from multiple broadcasters with separate licenses. Multiplexing has made it possible for many new free-to-air television services to be introduced, some of them expressly designed for carriage as additional channels. In the United States, such services are called digital multicast television networks or diginets. The term is also used in an otherwise unrelated sense to refer to additional channels offered by premium pay television services, such as HBO, similar to its meaning with regard to movie theaters.
Fellgett's advantage or the multiplex advantage is an improvement in signal-to-noise ratio (SNR) that is gained when taking multiplexed measurements rather than direct measurements. The name is derived from P. B. Fellgett, who first made the observation as part of his PhD. When measuring a signal whose noise is dominated by detector noise, a multiplexed measurement such as the signal generated by a Fourier transform spectrometer can produce a relative improvement in SNR, compared to an equivalent scanning monochromator, of the order of the square root of m, where m is the number of sample points comprising the spectrum.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Madam C.J. Walker