CHARACTER GENERATOR SELECT
Original Publication Date: 1985-May-01
Included in the Prior Art Database: 2005-Feb-18
This article describes an arrangement which selects between different character generators in alpha mode and an image overlay in graphics mode. Better use is made of available screen buffer memory so that the character generator is expanded from 256 to 512 characters. The arrangement, disclosed herein, is used in a display adapter with an expandable screen memory buffer. Fig. 1 illustrates the screen memory buffer organization. The configuration of the screen memory provides four-bit planes of 16K x 8 (each) which can be expanded by 16K increments up to 64K (each plane). Addressing for the expanded portion of the memory is provided by using the column address strobe (CAS) lines. ACAS lines control planes 0 and 1, and BCAS lines control planes 2 and 3.