Page
4.6
Software Considerations
Blanking/Clearing the Display
Blanking the display means that the characters stored
in
the character
memory are not displayed on the CRT. The memory
is
not affected and
can
be read or changed while the screen
is
blanked. The display
is
cleared
when all data stored
in
the RAM
is
erased.
The display
is
blanked through the video control register. To blank the
display, write XXXX
OXX1
(for example,
01
H)
to I/O address 3B8H. No
characters will be displayed on the CRT but the
RAM
may be changed
at this time.
The display
is
cleared by writing
Os
to all
RAM
locations.
Scrolling the Display
When
the standard 2K x 8 RAMs are installed, the display must be
scrolled by manipulating the data
in
the
RAM.
To scroll the display with
the standard RAM, data from location
81
must
be
moved to location
1,
etc.
When the optional 8K x 8
RAM
is
installed, the programmer can
use
the flexibility ofthe 6845 CRTC to scroll the display.
To Next Page