Modes Of Operation; Alphanumeric Mode - HP Vectra Reference Manual

Modes of Operation
The mode control register determines the mode of operation. The
following is a list of availabe RAM access modes.
*
Alphanumeric Mode
80
x
25
40
x
25
*
Graphics Mode
640 x 1
320 x 2
Alphanumeric Mode
When the HP45981A is set in the alphanumeric mode, words
(attribute byte
+
character byte) are fetched from the memory
starting at the offset programmed into the 6845 CRT controller.
This address is a word pointer and will always be used to fetch
from even byte boundaries. Words are fetched contiguously from
memory. For an 80 x 25 display, 2000 words (8 pages) are
fetched. For a 40 x 25 display, 1000 words (16 pages) are fetched.
The character code is a byte with the ASCII code for the character.
The attribute byte is defined as:
07 06 05 04 03
~
02 01 DO
W-J
Foreground color (R-G-B)
Foreground Intensity
Background color (R-G-B)
Background intensity/Blink
If underline enable is set, an underline will be generated for any
character with a foreground color of 001, and the color of the
character will be forced to 111 . If underline enable is not set the
character will be displayed as blue or a gray level.
88 Multi-Mode Video Adapter Card