Display apparatus

Claim 2

Display system having a character generator which is operable to generate a horizontal slice of a certain character pattern on a display screen of preferably a CRT in response to a character code and a line count of a line counter which is synchronized with a raster scan, the improvement characteized by first means for storing a control information to indicate a partition to be scrolled on a screen; second means connected to said first means for generating a scroll area signal when said partition is scanned; third means for retaining an offset data; fourth means connected to the output of said line counter, second and third means, responsive to said scroll area signal for selectively modifying said line count by adding said offset data to the line count and control means for changing said offset data in said third means.

Claim 3

Display apparatus with vertical scrolling facility especially as in claim 1 having a storage device (4) for storing a plurality of character codes for characters to be displayed on a display screen such as a screen of a CRT in connection with display rows, a column counter (55) for generating a column count output indicating successive character display columns in synchronism with the horizontal scanning of said screen, a line counter (61) for incrementing each time said column count output reaches a predetermined value to generate a line count output indicating successive scanning lines, an address device (5) for reading character codes successively out of said storage device in synchronism with said column counter and line counter, and a character generator (3) for transmiting a sequence of bits corresponding to a horizontal part of a corresponding character pattern in accordance with each character code read out of said storage device and said line count output, said display apparatus characterized by a control information holding means for holding control information defining a display column range and a display row range of an area wherein vertical smooth scrolling is to be performed in said screen, a signal generator means connected to said control information holding means, column counter and line counter for generating a smooth scroll area signal only during the time the area defined by said control information is scanned, an offset data holding means for holding offset data indicating the vertical shift amount for the vertical smooth scrolling, a modification means connected to said line counter, signal generator means and offset data holding means for modifying said line count output only during the generation of said smooth scroll area signal to provide a modified line count output, and a control means which can adequately modify said offset data and said control information, wherein said address means comprises a first row counter for incrementing each time said line count output reaches a predetermined value, a second row counter for incrementing each time said corrected line count output reaches a predetermined value, and a means connected to said control information holding means for instructing to read the character codes for the display row indicated by the row count of said second row counter within the display column range of the area subjected to the vertical smooth scrolling and for instructing to read the character codes for the display row indicated by the row count of said first row counter within the other display column range.

Claim 4

Display apparatus as in claim 1 or 2, wherein smooth scrolling can be performed in different areas of said screen by establishing the appropriate offset data and control information.