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The aim of this project is to design a Moving Message Display System of the type commonly seen in shop windows, airports, and other public buildings. The display will be required to be able to scroll a message from right to left, with at least eight characters on screen at any instant. Other display features (such as flashing text) will not be needed, since it would be extremely difficult to add these using ordinary logic ICs. An EPROM is used to store the message to be displayed on the LED display. Bits from the EPROM output correspond to the seven LED's in one column of the display. A high output turns an LED on, the LED display being a common cathode type. In order to scroll the message across the screen, the cathodes (displqy columns) of the LED's are scanned by the Cathode Multiples Block at a speed high enough so that the flickering cannot be seen. As each column is selected, the corresponding data for the LED anodes (display rows) is output from the EPROM and the main Address Counter is incriminated. After a number of scans set by the Scan counter, the Base Address Counter is incriminated and the new value loaded into the Main Address Counter. This sequence gives the issusion of the message scrolling across the display. The system has a single clock which is effectively divided down by each block
 
 

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