Interrupt Descriptions - Nintendo DMG-01 - Game Boy Console Manual

2.12.2. Interrupt Descriptions

2.12.2. Interrupt Descriptions
The following interrupts only occur if they have been
enabled in the Interrupt Enable register ($FFFF) and
if the interrupts have actually been enabled using the
EI instruction.
1. V-Blank
The V-Blank interrupt occurs ~59.7 times a second
on a regular GB and ~61.1 times a second on a Super
GB (SGB). This interrupt occurs at the beginning of
the V-Blank period. During this period video
hardware is not using video ram so it may be freely
accessed. This period lasts approximately 1.1 ms.
2. LCDC Status
There are various reasons for this interrupt to
occur as described by the STAT register ($FF40). One
very popular reason is to indicate to the user when
the video hardware is about to redraw a given LCD
line. This can be useful for dynamically controlling
the SCX/SCY registers ($FF43/$FF42) to perform
special video effects.
3. Timer Overflow
This interrupt occurs when the TIMA register ($FF05)
changes from $FF to $00.
4. Serial Transfer Completion
This interrupt occurs when a serial transfer has
completed on the game link port.
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Game Boy CPU Manual
V 1.01