GameBoy Video-Interupts v0.01                                    201299/GPZ-HIT
-------------------------------------------------------------------------------


Type      priority       jumps to

V-Blank   highest        $0040
LCDC         .           $0048
Timer        .           $0050
serial       .           $0058
pad       lowest         $0060


general IRQ registers:
----------------------

$ffff   (rIE)   IRQ Enable (read/write)

                bit:

                7-5     ?
                4       Transition High=>Low Pin P10-P13   0:disabled 1:enabled
                3       serial i/o transfer complete       0:disabled 1:enabled
                2       Timer overflow                     0:disabled 1:enabled
                1       LCDC                               0:disabled 1:enabled
                0       V-Blank                            0:disabled 1:enabled

$ff0f   (rIF)   IRQ Flag (read)

                - if an interupt has occured, this register tells what kind
                  of interupt it was.

                bit:

                7-5     ?
                4       Transition High=>Low Pin P10-P13
                3       serial i/o transfer complete
                2       Timer overflow
                1       LCDC
                0       V-Blank

LCDC IRQ-Registers:
-------------------

$ff44   (rLY)   LCDC Y-Coordinate

                read:   current Rasterline
                write:  reset lcd-y counter

$ff45   (rLYC)  LY-Compare (read/write)

                - if rLYC = rLY then bit 2 of rSTAT is set

$ff41   (rSTAT) LCDC Status

                bit:

                7       ?

                        IRQ source selection:

                6       rLYC=rLY                           <
                5       mode %10 (searching OAM)           |  write
                4       mode %01 (V-Blank)                 |
                3       mode %00 (H-Blank)                 <

                2       rLYC=rLY Flag                      <
                                                           |
                1-0     current mode:                      |
                                                           |
                        %00     H-Blank                    |  read
                        %01     V-Blank                    |
                        %10     searching OAM              |
                        %11     transfering data to LCD    <