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Device for displaying characters and graphs in superposed relation

  • US 4,491,832 A
  • Filed: 02/01/1982
  • Issued: 01/01/1985
  • Est. Priority Date: 02/13/1981
  • Status: Expired due to Fees
First Claim
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1. A display device comprising:

  • display memories for storing character codes and graphic images corresponding to characters and graphs to be displayed in superposed relation on a screen of a raster-scan type cathode ray tube;

    first and second parallel-to-serial converters for reading out plural-bit parallel graphic data and plural-bit parallel character data from said display memories in synchronism with a raster-scan timing of said tube in order to output graphic serial data and character serial data respectively;

    logic means for logically combining the output graphic serial data and character serial data to produce a video signal to be applied to said cathode ray tube;

    a fixed oscillator for generating and applying a first parallel-to-serial conversion control clock signal to said first parallel-to-serial converter;

    a PLL circuit for generating and applying a second parallel-to-serial conversion control clock signal to said second parallel-to-serial converter;

    means for generating first and second data load signals to cause respective data read-out operations of said first and second converters and for synchronizing said PLL circuit by comparing generated first and second data load signals to selectively produce any of a plurality of numbers of displayed character dots which may be different from a number of displayed graphic dots, whereby the character font of displayed characters can be freely changed irrespective to graphic dots.

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