Method and apparatus for improving the clarity and character density on a dot matrix video display

摘要

A method and apparatus is shown for improving the clarity and character density on a cathode ray tube (CRT) display in which characters are formed row by row from discrete character elements in row and column coordinate matrices. Unblanking signals form the discrete character elements no less than two matrix spaces wide every time an unblanking signal is applied. This technique results in a much crisper appearance to the characters on the screen and permits as many as 128 characters per line using a low cost commercially available television (TV) monitor. A random access storage is used to store dynamically the addresses of positions (locations) of a read only store corresponding to characters to be displayed. The read only store (ROS) contains indicia corresponding to the discrete character elements of a plurality of characters, one set of indicia for each character in the desired character set. Each addressable location of the ROS stores unblanking indicia (a plurality of bits) for the discrete character elements of one row of a character. The random access store in conjunction with timing means selects the ROS locations in sequence to form a row of characters on the display in accordance with the data read from the ROS. As each row of unblanking indicia or data is read from the ROS, it is entered into a shift register for transfer to the unblanking circuit of the display in bit serial form. Timing of the stores and shift register is controlled by a clock and suitable frequency dividers.