IA63484
Data Sheet
Advanced CRT Controller
background screens are superimposed on the display. Figure 3 is an example of the screen
combinations.
Figure 3: Screen Combination Examples
Screen Number
Screen Name
Upper Screen
Base Screen
Screen Group
0
1
Background Screen
2
3
Lower Screen
Window Screen
Upper
Base
Base
Window
Window
Lower
Upper
Upper
Base
Base
Window
Lower
Window
Lower
Display Control:
The ACRTC can have two types of external frame memory: 2 Mbyte frame buffer and 128 kbyte
refresh memory. The chr signal controls which memory is accessed.
Each screen has its own memory width, vertical display width, and character/graphic attribution set
by the control registers. Horizontal display control registers are set in units of memory cycles.
Vertical display control registers are set in units of rasters. Figure 4 illustrates the relation between the
frame memory and the display screens, while Figure 5 illustrates the timing.
Note that display width of registers marked with an (*) in Figure 4 is:
Display width = Register value + 1 memory cycle.
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