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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 of the 6845 CRTC to scroll the display.
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