Memory control unit in a display apparatus having a buffer memory

A memory control unit in a display apparatus comprising:

• (a) first memory means for storing character codes to be displayed over a plurality of rows on a display screen while scanning a raster;
• (b) first address means for designating addresses for reading out character codes stored in said first memory means during a horizontal flyback period of a raster scan;
• (c) second memory means having at least first and second memory areas, said second memory means storing said character codes read out of said first memory means in groups corresponding to a display row in said respective first and second memory areas;
• (d) second address means for designating the addresses of the character codes to be written in said second memory means;
• (e) third address means for designating the addresses of the character codes for reading out the character codes stored in said second memory means;
• (f) address switching means carrying out an address switching function for applying the address from said third address designating means to said first or second memory area in said second memory means during the period of displaying a row with the raster scan on the display screen, while applying the address from said second address designating means to said first or second memory area in said second memory means during a predetermined time within the horizontal flyback period;
• and
• (g) memory area switching means for providing read and write addresses to said first and second memory areas alternately with successive display of character rows on said display screen so that said addresses from said second and said third address means are applied respectively to said first and second memory areas.

A memory control unit in a display apparatus for displaying character patterns with raster scanning over a plurality of rows on a display screen comprising:

• (a) first memory means for storing coded data designating a plurality of character patterns;
• (b) first address counter means for designating addresses to said first memory means for reading therefrom coded data corresponding to character patterns to be displayed in the row next to that of data currently being displayed on said display screen;
• (c) an address bus for transmitting addresses of data for writing and reading out data into and from said first memory means;
• (d) a data bus for transmitting data to be written in at least said first memory means;
• (e) first address switching means for applying the address from said first address counter means to said first memory means during a first predetermined time within the horizontal flyback period of the raster scan on the display screen, and, on the other hand, applying the addresses from said address bus to said first memory means during a second predetermined time other than said first predetermined time;
• (f) row counter means for sequentially counting the number of character rows on the display screen;
• (g) second memory means including a first memory area and a second memory area for storing data read out of said first memory means to be displayed in each of the adjacent rows on the display screen;
• (h) second address counter means for selectively designating the addresses of said first memory area or said second memory area for writing the data read out of said first memory means to be written in said buffer memory;
• (i) third address counter means for selectively designating the addresses in said first memory area or said second memory area for reading out the data stored in said second memory means;
• (j) second address switching means for applying the address from said third address counter means to said first or second memory area during the display period of a character row with the raster scan on the display screen and, on the other hand, applying the address from said second address counter means to said first or second memory area during a time within horizontal flyback periods of the raster scan;
• and
• (k) memory area switching means for applying addresses alternately to the first and second memory areas accessed by said second and third address counter means in accordance with the output of said row counter means.

A character data processing unit for displaying character patterns by raster scanning a plurality of character rows on a screen of a cathode-ray tube, comprising:

• (a) refresh memory means for storing character data to be displayed as a plurality of character patterns;
• (b) first address counter means for sequentially applying addresses to said refresh memory means so that, during scanning of a character row on the CRT screen, data to be displayed in a row next to said row can be read out of said refresh memory means;
• (c) an address bus for transmitting addresses for writing and reading out data in and from said refresh memory means;
• (d) a data bus for transmitting data written in and read out of said refresh memory means;
• (e) first address selecting means for selecting the address from said first address counter means during a predetermined time within the horizontal flyback period of the raster scan and, on the other hand, selecting the address from said address bus during a time other than said predetermined time, thereby permitting access to said refresh memory means according to the address so selected;
• (f) row counter means for sequentially counting the number of character rows on the CRT screen;
• (g) buffer memory means including a first row buffer and a second row buffer for sequentially storing the data in each of adjacent character rows read out of said refresh memory means;
• (h) second address counter means designating the addresses of said row buffer or said second row buffer for writing the data read out of said refresh memory means in said buffer memory means;
• (i) third address counter means designating the addresses of said second row buffer or said first row buffer for reading out the data written in said buffer memory means;
• (j) second address selecting means for selecting the address from said third address counter during the display period of the raster scan of a character row on the CRT screen, and, on the other hand, selecting the address from said second address counter during the predetermined time within the horizontal flyback period, thereby permitting access to said buffer memory means according to the address so selected;
• and
• (k) row buffer switching means for selecting said first and second row buffers, thereby exchanging a row buffer to be accessed by said second address counter means for a row buffer to be accessed by said third address counter means, at each incrementing of said row counter means.