Display controller

• US 5,521,613 A
• Filed: 03/21/1994
• Issued: 05/28/1996
• Est. Priority Date: 02/12/1991
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation), Mitsubishi Electric Corporation
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Hayashi, Kazuo
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): NGUYEN, CHANH DUY
• Application Number:
  US08/215,404
• Time in Patent Office: 799 Days
• Field of Search: 340/748, 340/750, 340/790, 340/721, 358/160, 358/183, 345/25, 345/26, 345/27, 345/28, 345/141, 345/116, 345/200, 345/192, 345/194, 348/563, 348/564
• US Class Current: 345/563
• CPC Class Codes: G09G 5/42 characterised by the display of patterns using a display memory without fixed position correspondence between the display memory contents and the display position on the screen

Abstract

To minimize the capacity of a random access memory for storing display data of a display controller for displaying characters or the like on a television screen, the display data is divided into the data for characters or the like and the blank data free from characters with a discriminator, the data for characters or the like are stored in the random access memory every unit address, the number of non-characters shown by the blank data is counted by a counter, and the cumulative counted number is stored in the unit address of the random access memory. When the blank data is displayed, the counted number is read from the random access memory and non-character signals equivalent to the counted number are output to a display unit.

Claims

1. A display controller for displaying characters, such as channel numbers and operating modes, on a television screen that receives characters to be displayed and blanks indicating that no character is to be displayed, for sectioning the television screen into unit areas and for controlling the television screen to display a character or blank in each unit area,, said display controller comprising:

a discriminator, that receives characters and blanks to be displayed, and asserts a first signal only when a blank is received;

an input counter and flag register, having an input coupled to said discriminator, for setting a flag value to a set flag value in said flag register and incrementing a count value whenever said first signal is asserted to generate a repetition value and for resetting said flag value to a reset flag value and said count value to zero when said first signal is not asserted;

a random access memory (RAM) having a plurality of addressable storage locations, each addressable storage location having a flag area for storing flag data and a data area for storing character data, with character data specifying either a received character or a repetition value specifying a number of repeated blanks to be displayed on the television screen;

a write-control circuit, coupled to said discriminator and input counter and flag register and responsive to said first signal, for, when a received character other than a blank is received at said discriminator causing said first signal not to be asserted and when said flag value has been previously set, writing only said set flag value, to said flag area of a first addressable storage location, and a repetitive value, indicating a number of successive blanks, as character data to the data area of said first addressable storage location in said RAM, prior to the resetting of said flag and count values in said input counter and flag register, and for writing a reset flag value to said flag area of a second addressable storage location and said received character as character data to the data area of said second addressable storage location in said RAM after said flag value is reset;

a character ROM for receiving character data as address data and providing fonts as output data;

an output counter, coupled to said RAM, for receiving said flag data from the flag area and said character data from the data area of a selected storage location and, when said received flag data is equal to the set flag value, for setting its count value to a set count value equal to the repetition value stored in the data area of said selected storage location as character data, for asserting a second signal when said set count signal has a non-zero value, and for decrementing the set count value subsequent to asserting the second signal and, when said received flag data is equal to the reset flag value, and for transferring a received character stored in the selected storage locations as character data to the character ROM;

a control circuit, coupled to said output counter to receive said second signal, for asserting a third signal whenever said second signal is asserted; and

a display control circuit, having inputs coupled to said character ROM and said control circuit, for causing said display unit to display a blank when said third signal is asserted and to display a font, addressed by a character retrieved from the selected storage location as non-flag data, from said character ROM when the third signal is not asserted.