Modes Of Operation - Zenith Z-100 Reference Manual

Page 7.9
Video Graphics Programming

Modes of Operation

The video card can operate in one of two major modes: text mode and pixel
addressable graphics mode. Additional submodes are available within each mode,
for either color or monochrome display.
Text Mode
In text mode, the display formats in either a 40-column by 25-line submode,
or in an 80-column by 25-line submode. In either submode, characters are formed
in an 8 x 8 character matrix.
In either submode, the characters take up a 7 x 7 portion of this matrix space
with one line for descenders in lowercase characters. Both uppercase and lowercase
characters are available in all modes.
On a monochrome monitor, reverse video, blinking, sixteen foreground and back-
ground levels of gray, and highlighting features can be obtained on an individual
character basis. On an RGB monitor, sixteen foreground, background, or border
colors, blinking, and highlighting are available on a per-character basis.
Using 40 x 25 resolution requires 1000 bytes for character information storage
and 1000 bytes for attribute information for one screen (page) of information.
Since there is 16K of video memory, up to eight screens can be stored in video
memory. Also, since all the video memory is directly addressable by the CPU,
extreme flexibility in manipulation of screen contents is obtainable.