Browse Prior Art Database

Segmented Use of All-Points-Addressable Memory in Graphic Mode

IP.com Disclosure Number: IPCOM000042431D
Original Publication Date: 1984-May-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 3 page(s) / 76K

Publishing Venue

IBM

Related People

Nakano, Y: AUTHOR [+2]

Abstract

The present display adapter includes an all-points-addressable (APA) memory which is selectively used as a character generator or as an APA refresh buffer depending on whether the system is in character mode or graphic mode. In graphic mode, the APA memory is segmented into two blocks, whereby graphics and character data separately provided from the segmented blocks are allowed to co-exist throughout the entire cathode ray tube (CRT) screen. A latch circuit arrangement is provided in this display adapter for controlling wrap functions in the segmented blocks. Referring to Fig. 1, the present display adapter 10 is coupled by the system bus to a conventional central processing unit (CPU) 12 and by another bus to a CRT display 14.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 52% of the total text.

Page 1 of 3

Segmented Use of All-Points-Addressable Memory in Graphic Mode

The present display adapter includes an all-points-addressable (APA) memory which is selectively used as a character generator or as an APA refresh buffer depending on whether the system is in character mode or graphic mode. In graphic mode, the APA memory is segmented into two blocks, whereby graphics and character data separately provided from the segmented blocks are allowed to co-exist throughout the entire cathode ray tube (CRT) screen. A latch circuit arrangement is provided in this display adapter for controlling wrap functions in the segmented blocks. Referring to Fig. 1, the present display adapter 10 is coupled by the system bus to a conventional central processing unit (CPU) 12 and by another bus to a CRT display 14. For sake of example, it is assumed that the CRT screen comprises 512 lines, with each line having 512 dot positions. Thus, 32K bytes of data will be necessary for completing the image on the CRT screen. As well known in the art, the display adapter 10 includes a code refresh memory 16 paired with an attribute memory 18 which may be operated in character mode to serially provide character codes to an APA memory 20, used as a character generator in this mode, to cause each of the character data derived therefrom to be displayed on the CRT 14. In graphic mode, however, both the code refresh memory 16 and the attribute memory 18 are disabled so that the APA memory 20 alone is used as an APA refresh memory by means of a CRT controller 22 which provides the control and addressing of the APA memory
20. In order to label graphics or plots on the CRT screen, it is desirable in graphic mode to concurrently display both the graphics and character data on the CRT screen without degrading system performance. This can be accomplished by logically segmenting the APA memory 20 into two 64K byte blocks, as shown in Fig. 2A, which for simplicity illustrates only a single segmentation. In this example, the upper 64K-byte block including the screen window area is used to contain graphics data while the lower 64K-byte block is used to contain character data. Thus, all graphics data during a graphic frame comes from the screen window area in the upper 64K-byte block. On the other hand, when a given character, such as "A", is to be appended to graphics or plots on the CRT sc...