Servicing Personal Computers, 3rd Edition

Microcomputer systems 65

display, providing various programmable screen and character formats, and generating

synchronizing and blanking signals. Characters to be displayed are usually retrieved from

memory and displayed on a row-by-row basis. Direct memory access (DMA) techniques are

used to permit fast data transfer without requiring the attention of the CPU. Internal registers

are provided to buffer several lines of the display during scanning. The process of building up

lines of the display is illustrated in Figure Ί .70. Note that although this example shows a row

of 40 8 x 8 characters, both the number of characters per row and the compositio ...