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CHAPTER 18 OSDC
18.3.6
Interrupt Control
There are three factors of OSDC control interrupt:
• Detection of line display end
• Detection of vertical synchronization signal
• Detection of VRAM fill end
An interrupt request is issued to the CPU when any of the three factors occurs.
■ Interrupt Control
Interrupt control is used to control the interrupts generated by the internal operation status.
Interrupt control is performed according to the interrupt factor flags and interrupt generation
control bits of the interrupt control command (command 15-0).
■ Interrupt Factor Flags
Each interrupt factor flag is set to 1 when the relevant factor occurs.
To clear a set interrupt factor flag, it is set to 0.
There are three interrupt factor flags:
•
Line display end flag (bit LIF of command 15-0)
•
Vertical synchronization signal input flag (bit VIF of command 15-0)
•
VRAM fill end flag (bit FIF of command 15-0)
❍ Line display end flag
The last raster of each line and a line end detection line for the top-line immediately start raster
part as shown in Figure 18.3-15 becomes a factor of line display end.
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