Abstract: In a CRT display system, its screen is divided into a least two partitions or viewports for displaying different data groups, and characters in one of the groups can be vertically scrolled bit by bit in one of the partitions. The partition to be scrolled is defined by line attributes assigned to successive rows of the screen. When a raster scan passes the scrolling partition, a line count output of a (scan) line counter is modified by adding a content of a smooth scroll offset register to the line count. The modified line count is used together with a character code as an address for a character generator. By gradually changing the content of the offset register, the characters are vertically shifted smoothly in the partition.

Abstract: A digital display system includes a refresh store containing character data for display on a raster scan video display device and field attribute data defining attributes of fields of the character data. The character data is stored as character bytes in sequential locations in the store for readout in groups to provide respective rows of displayed characters. The field attribute data comprises attribute bytes interspersed with the character bytes. Character bytes in a group read out following an attribute byte provide displayed characters with an attribute defined by that attribute byte until another attribute byte is accessed in the group. In order to maintain an attribute from one row of displayed characters to the next, the group of character bytes corresponding to the next row requires a copy attribute byte at the start of readout of that group.