Browse Prior Art Database

Move Controller for Refresh Matrix Buffer of CRT Display

IP.com Disclosure Number: IPCOM000052010D
Original Publication Date: 1981-Apr-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 3 page(s) / 63K

Publishing Venue

IBM

Related People

Ringle, TW: AUTHOR [+2]

Abstract

Two move controllers are provided for a refresh matrix buffer of a CRT display, the first to effect columnar movement and the second to effect row movement, the use of the controllers thereby effecting a scroll right/left or a scroll up/down motion. The move controller is also utilized to move characters from a special font table to the buffer, thereby freeing the host processor from this chore.

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Move Controller for Refresh Matrix Buffer of CRT Display

Two move controllers are provided for a refresh matrix buffer of a CRT display, the first to effect columnar movement and the second to effect row movement, the use of the controllers thereby effecting a scroll right/left or a scroll up/down motion. The move controller is also utilized to move characters from a special font table to the buffer, thereby freeing the host processor from this chore.

Raster Scan CRT Display controllers can be classified into two categories:
(1) Dot Matrix Character Generators and (2) Picture Element Display Controllers. Picture Element Display Controllers contain a large matrix refresh buffer which fully buffers the entire CRT image with a binary bit in the RAM (random-access memory) buffer corresponding to each picture element. The major problem with this bit map approach is the burden it places on the host processor to manipulate the buffer contents. Even with a dedicated processor, the update speed is often too great to make this approach applicable to word processing applications. The move controller described herein relieves the host processor of much of the burden of manipulating a bit matrix buffer while increasing the update speed to a point that is acceptable in a word processing display.

The refresh matrix move controller 11 operates transparent to the host processor to allow the host to do other data manipulation while the refresh buffer 13 is being updated. Move controller 11 also operates transparent to the normal display refresh memory cycle so that flicker does not occur when the matrix is manipulated. To accomplish this, the refresh buffer is shared between the driving system and the display refresh controller. Both the host processor and move controller 11 access the refresh buffer 13 as the driving system. When move controller 11 is executing, the host system can operate on any other memory space but does not have access to the refresh buffer until the move is completed. When the move controller 11 is finished, the host processor can either be interrupted or check the status byte of the interface. Control 15 effects this time sharing.

Functionally, move controller 11 moves scan lines "up or down" in the matrix of data stored in buffer 13 and moves columns of data "left and right" in the matrix. Sixty-four bytes of the matrix define one scan line, allowing 256 scan lines in a 16K X 8 refresh buffer to be defined. This size buffer gives the host processor a 512 X 256 bit matrix that must be manipulated to form the pattern to be displayed on the CRT by video generator 17. Two move functions are defined. The Row Move is used when entire scan rows or portions of scan rows are moved up or down in the matrix. The Column Move is used when entire columns or portions of columns are moved left or right in the matrix. In each case, three 16-bit registers define the parameters of the move: (1) Move From,
(2) Move To, and (3) Stop Move. The l...