Nintendo GAME BOY Programming Manual page 58

Game Boy Programming Manual
NAME ADDRESS
STAT FF41h
STAT indicates the current status of the LCD controller.
Mode 00: A flag value of 1 represents a horizontal blanking period and means that the CPU has
access to display RAM (8000h-9FFFh).
When the value of the flag is 0, display RAM is in use by the LCD controller.
Mode 01: A flag value of 1 indicates a vertical blanking period and means that the CPU has
access (approximately 1 ms) to display RAM (8000h-9FFFh).
Mode 10: A flag value of 1 means that OAM (FE00h-FE90h) is being used by the LCD
controller and is inaccessible by the CPU.
Mode 11: A flag value of 1 means that the LCD controller is using 0AM (FE00h-FE90h) and
display RAM (8000h-9FFFh).
In addition, the register allows selection of 1 of the 4 types of interrupts from the LCD controller.
Executing a write instruction for the match flag resets that flag but does not change the mode
flag.
NAME ADDRESS
SCY FF42h
NAME ADDRESS
SCX FF43h
BIT 7 6 5 4
The CPU cannot access either of these areas.
BIT 7 6 5 4
BIT 7 6 5 4
3 2 1 0
R/W
Mode Flag
00: Enable CPU Access to all Display RAM
01: In vertical blanking period
10: Searching OAM RAM
11: Transferring data to LCD Driver
Match Flag
0: LYC = LCDC LY
1: LYC = LCDC LY
Interrupt Selection According to LCD
Status
Mode 00 Selection
Mode 01 Selection, 0: not selected
Mode 10 Selection, 1: selected
LYC = LY matching selection
3 2 1 0
3 2
1 0
58
LCD Status Flag
Scroll Y
R/W
00~FF
Scroll X
R/W
00~FF