Nintendo DMG-01 Manual - Page 53
used $FE00-$FE9F. The CPU cannot access - drivers
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Game BoyTM CPU Manual 2.13.1. I/O Registers Bit 6 - LYC=LY Coincidence (Selectable) Bit 5 - Mode 10 Bit 4 - Mode 01 Bit 3 - Mode 00 0: Non Selection 1: Selection Bit 2 - Coincidence Flag 0: LYC not equal to LCDC LY 1: LYC = LCDC LY Bit 1-0 - Mode Flag 00: During H-Blank 01: During V-Blank 10: During Searching OAM-RAM 11: During Transfering Data to LCD Driver STAT shows the current status of the LCD controller. Mode 00: When the flag is 00 it is the H-Blank period and the CPU can access the display RAM ($8000-$9FFF). Mode 01: When the flag is 01 it is the V-Blank period and the CPU can access the display RAM ($8000-$9FFF). Mode 10: When the flag is 10 then the OAM is being used ($FE00-$FE9F). The CPU cannot access the OAM during this period Mode 11: When the flag is 11 both the OAM and display RAM are being used. The CPU cannot access either during this period. The following are typical when the display is enabled: by DP Page 53