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Gameboy Programming Info
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| Programming Info | |
| Information about GameBoy hardware and programming is extremely hard to find. Most of it is incomplete, uncertain and vague. If you have any new information, PLEASE, email it to me. The following information is mostly based on a document by Pan of Anthrox, Jeff Frohwein's, Pascal Felber's, and my own findings. | |
| Memory Map | |
| --------------------------- FFFF | 32kB ROMs are non-switchable and occupy | |
| I/O ports + internal RAM | 0000-7FFF are. Bigger ROMs use one of two | |
| --------------------------- FF00 | different bank switches. The type of a | |
| Internal RAM | bank switch can be determined from the | |
| --------------------------- C000 | internal info area located at 0100-014F | |
| 8kB switchable RAM bank | in each cartridge. | |
| --------------------------- A000 | | |
| 16kB VRAM | MBC1 (Memory Bank Controller 1): | |
| --------------------------- 8000 | Writing a value into 2000-3FFF area will | |
| 16kB switchable ROM bank | select an appropriate ROM bank at | |
| --------------------------- 4000 | 4000-7FFF. Writing a value into 4000-5FFF | |
| 16kB ROM bank #0 | area will select an appropriate RAM bank | |
| --------------------------- 0000 | at A000-C000. | |
| | | |
| | MBC2 (Memory Bank Controller 2): | |
| | Writing a value into 2100-21FF area will | |
| | select an appropriate ROM bank at | |
| | 4000-7FFF. RAM switching is not provided. | |
| CPU | |
| As it appears, the CPU used in GameBoy is not exactly Z80. Some of Z80 instructions and registers are missing while others are added: | |
| The "shadow" set of registers (BC',DE',HL',AF') and the index registers (IX,IY) are missing and, consequently, there are no DD and FD opcode tables. | |
| I/O ports are gone and so are all IN/OUT opcodes. | |
| HALT is interrupted even when interrupts are disabled. | |
| Following Z80 opcodes are changed: | |
| ------------------------------------------------------------------------------ | |
| Code Z80 operation GameBoy operation | |
| ------------------------------------------------------------------------------ | |
| 08 xx xx EX AF,AF' LD (word),SP Save SP at given address | |
| 10 xx DJNZ offset STOP Meaning unknown | |
| 22 LD (word),HL LD (HLI),A Save A at (HL) and increment HL | |
| 2A LD HL,(word) LD A,(HLI) Load A from (HL) and increment HL | |
| 32 LD (word),A LD (HLD),A Save A at (HL) and decrement HL | |
| 3A LD A,(word) LD A,(HLD) Load A from (HL) and decrement HL | |
| D3 OUTA (byte) No operation | |
| D9 EXX RETI Enable interrupts and return | |
| DB INA (byte) No operation | |
| DD Prefix DD No operation | |
| E0 xx RET PO LD (byte),A Save A at (FF00+byte) | |
| E2 JP PO,word LD (C),A Save A at (FF00+C) | |
| E3 EX HL,(SP) No operation | |
| E4 CALL PO,word No operation | |
| E8 xx RET PE ADD SP,offset Add signed offset to SP | |
| EA xx xx JP PE,word LD (word),A Save A at given address | |
| EB EX DE,HL No operation | |
| EC CALL PE,word No operation | |
| F0 xx RET P LD A,(byte) Load A from (FF00+byte) | |
| F2 JP P,word No operation | |
| F4 CALL P,word No operation | |
| F8 xx RET M LDHL SP,offset Load HL with SP + signed offset | |
| FA xx xx JP M,word LD A,(word) Load A from given address | |
| FC CALL M,word No operation | |
| FD Prefix FD No operation | |
| ------------------------------------------------------------------------------ | |
| Internal information area | |
| The internal information area is located at 0100-014F in each cartridge. It contains following values: | |
| 0100-0103 A sequence of bytes 00 C3 xx xx where last two bytes contain the | |
| starting address of a cartridge (lower byte first). The first two | |
| bytes of this sequence can be used as a "magic number" to | |
| recognize GameBoy cartridges. When GameBoy starts, the control is | |
| passed to address 0100 and then the sequence is interpreted as | |
| NOP; JP . | |
| 0105-0133 Nintendo character area: | |
| CE ED 66 66 CC 0D 00 0B 03 73 00 83 00 0C 00 0D | |
| 00 08 11 1F 88 89 00 0E DC CC 6E E6 DD DD D9 99 | |
| BB BB 67 63 6E 0E EC CC DD DC 99 9F BB B9 33 3E | |
| 0134-0143 Title of the game in ASCII terminated by zeroes | |
| 0144-0145 Extended manufacturer code in ASCII, when 33 stored at 014B | |
| 0146 Not used | |
| 0147 Cartridge type: | |
| 0 - ROM ONLY 3 - ROM+MBC1+RAM+BATTERY | |
| 1 - ROM+MBC1 5 - ROM+MBC2 | |
| 2 - ROM+MBC1+RAM 6 - ROM+MBC2+BATTERY | |
| 0148 ROM size: | |
| 0 - 256kBit = 32kB = 2 banks | |
| 1 - 512kBit = 64kB = 4 banks | |
| 2 - 1MBit = 128kB = 8 banks | |
| 3 - 2MBit = 256kB = 16 banks | |
| 4 - 4MBit = 512kB = 32 banks | |
| 0149 RAM size: | |
| 0 - None | |
| 1 - 16kBit = 2kB = 1 bank | |
| 2 - 64kBit = 8kB = 1 bank | |
| 3 - 256kBit = 32kB = 4 banks | |
| 014A Language: | |
| 0 - Japanese game | |
| 1 - English game | |
| 014B Manufacturer code: | |
| 33 - Nintendo or extended (see 0144-0145) | |
| 79 - Accolade | |
| A4 - Konami | |
| 014C Version number | |
| 014D Complement check | |
| 014E-014F Checksum (higher byte first) produced by adding all bytes of | |
| a cartridge except for two checksum bytes together and taking | |
| two lower bytes of the result. | |
| Interrupts | |
| This section is not ready yet. | |
| Video | |
| The main GameBoy screen buffer (aka background) consists of 256x256 pixels or 32x32 tiles (8x8 pixels each). Only 160x144 pixels can be displayed on the screen. Registers SCROLLX and SCROLLY hold the coordinates of background to be displayed in the left upper corner of the screen. Background wraps around the screen i.e. when part of it goes off the screen, it appears on the opposite side. | |
| An area of VRAM known as Background Tile Table contains the numbers of tiles to be displayed. It is organized as 32 rows of 32 bytes each. Each byte contains a number of a tile to be displayed. Tile patterns are taken from the Tile Pattern Table located either at 8000-8FFF or 8800-97FF. In the first case, patterns are numbered with unsigned numbers from 0 to 255 (i.e. pattern #0 lies at address 8000). In the second case, patterns have signed numbers from -128 to 127 [i.e. pattern #0 lies at address 9000). The Tile Pattern Table address for the background can be selected via LCDCONT register. | |
| Besides background, there is also a "window" overlaying the background. The window is not scrollable i.e. it is always displayed starting from its left upper corner. The location of a window on the screen can be adjusted via WNDPOSX and WNDPOSY registers. Screen coordinates of the top left corner of a window are WNDPOSX-7,WNDPOSY. The tile numbers for the window are stored in the Window Tile Table in the same way as background tiles are stored in the Background Tile Table. The tile patterns are taken from the table at 8800-97FF and therefore have unsigned numbers. | |
| Both background and window can be disabled or enabled separately via bits in the LCDCONT register. | |
| The tile images are stored in the Tile Pattern Tables. Each 8x8 image occupies 16 bytes, where each 2 bytes represent a line: | |
| Tile: Image: | |
| .33333.. .33333.. -> 01111100 -> 7Ch | |
| 22...22. 01111100 -> 7Ch | |
| 11...11. 22...22. -> 00000000 -> 00h | |
| 2222222. <-- digits represent 11000110 -> C6h | |
| 33...33. color numbers 11...11. -> 11000110 -> C6h | |
| 22...22. 00000000 -> 00h | |
| 11...11. 2222222. -> 00000000 -> 00h | |
| ........ 11111110 -> FEh | |
| 33...33. -> 11000110 -> C6h | |
| 11000110 -> C6h | |
| 22...22. -> 00000000 -> 00h | |
| 11000110 -> C6h | |
| 11...11. -> 11000110 -> C6h | |
| 00000000 -> 00h | |
| ........ -> 00000000 -> 00h | |
| 00000000 -> 00h | |
| As it was said before, there are two Tile Pattern Tables at 8000-8FFF and at 8800-97FF. The first one can be used for sprites and the background. Its tiles are numbered from 0 to 255. The second table can be used for the background and the window display and its tiles are numbered from -128 to 127. | |
| Sprites | |
| GameBoy video controller can display up to 40 sprites either in 8x8 or in 8x16 mode. Sprite patterns have the same format as tiles, but they are taken from the Sprite Pattern Table located at 8000-8FFF and therefore have unsigned numbers. Sprite attributes reside in the Sprite Attribute Table (aka OAM) at FE00-FE9F. OAM is divided into 40 4-byte blocks each of which corresponds to a sprite. Blocks have the following format: | |
| Byte0 Y position on the screen | |
| Byte1 X position on the screen | |
| Byte2 Pattern number 0-255 [notice that unlike tile numbers, sprite | |
| pattern numbers are unsigned] | |
| Byte3 Flags: | |
| Bit7 Priority | |
| Sprite is displayed in front of the window if this bit | |
| is set to 1. Otherwise, sprite is shown behind the | |
| window but in front of the background. | |
| Bit6 Y flip | |
| Sprite pattern is flipped vertically if this bit is | |
| set to 1. | |
| Bit5 X flip | |
| Sprite pattern is flipped horizontally if this bit is | |
| set to 1. | |
| Bit4 Palette number | |
| Sprite colors are taken from OBJ1PAL if this bit is | |
| set to 1 and from OBJ0PAL otherwise. | |
| Sound | |
| There are two sound channels connected to the output terminals SO1 and SO2. There is also a input terminal Vin connected to the cartridge. It can be routed to either of both output terminals. GameBoy circuitry allows produces sound in four different ways: | |
| Quadrangular wave patterns with sweep and envelope functions | |
| Quadrangular wave patterns with envelope functions | |
| Voluntary wave pattern | |
| White noise | |
| These four sounds can be controlled independantly and then mixed separately for each of the output terminals. | |
| I/O Ports | |
| I/O ports are mapped to memory locations in FF00-FFFF area: | |
| ------------------------------------------------------------------------------ | |
| FF00 -- JOYPAD [RW] Joypad port | |
| Bit5 Bit4 | In order to scan the keys, output 0 into either Bit4 | |
| Bit3 DOWN START | or Bit5 of JOYPAD, wait for some time and read JOYPAD. | |
| Bit2 UP SELECT | Bits 0-3 will be set to zeroes if corresponding | |
| Bit1 LEFT B | buttons are pressed. Bits 6 and 7 are not used. Bits | |
| Bit0 RIGHT A | 0-3 are connected to input lines P10-P13. Bits 4 and 5 | |
| | are connected to ouput lines P14 and P15. | |
| Example: | |
| ; Routine finding which buttons were pressed since the last check | |
| LD A,20h ; Set 0 at the output line P14 | |
| LD (FF00h),A ; | |
| LD A,(FF00h) ; Read JOYPAD several times to accomodate the noise | |
| LD A,(FF00h) ; | |
| CPL ; Bits 0-3 are now 1s if corresponding buttons pressed | |
| AND 0Fh ; Extract lower 4 bits carrying button status... | |
| SWAP A ; ...and move them into upper for bits | |
| LD B,A ; At this point: B = START.SELECT.B.A.x.x.x.x | |
| LD A,10h ; Set 0 at the output line P15 | |
| LD (FF00h),A ; | |
| LD A,(FF00h) ; Read JOYPAD several times to accomodate the noise | |
| LD A,(FF00h) ; | |
| LD A,(FF00h) ; | |
| LD A,(FF00h) ; | |
| LD A,(FF00h) ; | |
| LD A,(FF00h) ; | |
| CPL ; Bits 0-3 are now 1s if corresponding buttons pressed | |
| AND 0Fh ; Extract lower 4 bits carrying buttons' status... | |
| OR B ; ...and combine them with 4 other button status bits | |
| LD D,A ; At this point: D = START.SELECT.B.A.DOWN.UP.LEFT.RIGHT | |
| LD A,(FF8Bh) ; Read old button status from RAM | |
| XOR D ; Set 1s for buttons whose status has changed | |
| AND D ; Extract buttons which were *pressed* since last check | |
| LD (FF8Ch),A ; Save information of those buttons | |
| LD A,D ; Update button status in RAM | |
| LD (FF8Bh),A ; | |
| LD A,30h ; Set 1s at both P14 and P15 lines | |
| LD (FF00h),A ; [probably to reset the circuitry] | |
| ------------------------------------------------------------------------------ | |
| FF01 -- SIODATA [RW] Serial I/O Data | |
| ----------------------------------------------+---------------+--------------- | |
| FF02 -- SIOCONT [RW] Serial I/O Control | when set to 1 | when set to 0 | |
| Bit7 Transfer start flag | START | NO TRANSFER | |
| Bit0 Serial I/O clock select | INTERNAL | EXTERNAL | |
| ----------------------------------------------+---------------+--------------- | |
| FF04 -- DIVIDER [RW] Divider [meaning unknown] | |
| ------------------------------------------------------------------------------ | |
| FF05 -- TIMECNT [RW] Timer Counter | |
| This register contains constantly increasing number. The timer | |
| interrupt occurs when this register overflows. | |
| ------------------------------------------------------------------------------ | |
| FF06 -- TIMEMOD [RW] Timer Modulo | |
| The contents of TIMEMOD are loaded into TIMECNT every time TIMECNT | |
| overflows. | |
| ----------------------------------------------+---------------+--------------- | |
| FF07 -- TIMCONT [RW] Timer Control | when set to 1 | when set to 0 | |
| Bit2 Start/Stop timer | COUNTING | STOPPED | |
| Bit1-0 Timer clock select: | |
| 00 - 4096Hz 01 - 262144Hz 10 - 65536Hz 11 - 16384Hz | |
| ----------------------------------------------+---------------+--------------- | |
| FF0F -- IFLAGS [RW] Interrupt Flags | when set to 1 | when set to 0 | |
| Bit4 Transition High->Low on pins P10-P13 | OCCURED | NO | |
| Bit3 End of serial I/O transfer | OCCURED | NO | |
| Bit2 Timer overflow | OCCURED | NO | |
| Bit1 LCD controller interrupt [see LCDSTAT] | OCCURED | NO | |
| Bit0 LCD vertical blanking impulse | OCCURED | NO | |
| ----------------------------------------------+---------------+--------------- | |
| FF10 -- SNDREG10 [RW] Sweep [Sound Mode #1] | |
| Bit6-4 Sweep time: | |
| 000: SWEEP OFF 010: 15.6ms 100: 31.3ms 110: 46.9ms | |
| 001: 7.8ms 011: 23.4ms 101: 39.1ms 111: 54.7ms | |
| Bit3 Frequency increase[0]/decrease[1] | |
| Bit2-0 Number of shifts | |
| ------------------------------------------------------------------------------ | |
| FF11 -- SNDREG11 [RW] Sound Length/Pattern Duty [Sound Mode #1] | |
| Bit7-6 Wave Pattern Duty [only these bits can be read]: | |
| 00: 12.5% 01: 25% 10: 50% 11: 75% | |
| Bit5-0 Length of sound data | |
| ------------------------------------------------------------------------------ | |
| FF12 -- SNDREG12 [RW] Control [Sound Mode #1] | |
| Bit7-4 Initial value of envelope | |
| Bit3 Envelope up[1]/down[0] | |
| Bit2-0 Number of envelope sweep | |
| ------------------------------------------------------------------------------ | |
| FF13 -- SNDREG13 [W] Frequency Low [Sound Mode #1] | |
| Lower 8 bits of the 11bit frequency. Higher 3 bits are in SNDREG14. | |
| ------------------------------------------------------------------------------ | |
| FF14 -- SNDREG14 [RW] Frequency High [Sound Mode #1] | |
| Bit7 When 1 is written into this bit, sound restarts | |
| Bit6 Counter/Consecutive selection [only this bit can be read] | |
| Bit2-0 Higher 3 bits of the 11bit frequency | |
| ------------------------------------------------------------------------------ | |
| FF16 -- SNDREG21 [RW] Sound Length/Pattern Duty [Sound Mode #2] | |
| Bit7-6 Wave Pattern Duty [only these bits can be read]: | |
| 00: 12.5% 01: 25% 10: 50% 11: 75% | |
| Bit5-0 Length of sound data | |
| ------------------------------------------------------------------------------ | |
| FF17 -- SNDREG22 [RW] Control [Sound Mode #2] | |
| Bit7-4 Initial value of envelope | |
| Bit3 Envelope up[1]/down[0] | |
| Bit2-0 Number of envelope step | |
| ------------------------------------------------------------------------------ | |
| FF18 -- SNDREG23 [W] Frequency Low [Sound Mode #2] | |
| Lower 8 bits of the 11bit frequency. Higher 3 bits are in SNDREG24. | |
| ------------------------------------------------------------------------------ | |
| FF19 -- SNDREG24 [RW] Frequency High [Sound Mode #2] | |
| Bit7 When 1 is written into this bit, sound restarts | |
| Bit6 Counter/Consecutive selection [only this bit can be read] | |
| Bit2-0 Higher 3 bits of the 11bit frequency | |
| ------------------------------------------------------------------------------ | |
| FF1A -- SNDREG30 [RW] Control [Sound Mode #3] | |
| Bit7 Sound on[1]/off[0] | |
| ------------------------------------------------------------------------------ | |
| FF1B -- SNDREG31 [RW] Sound Length [Sound Mode #3] | |
| ------------------------------------------------------------------------------ | |
| FF1C -- SNDREG32 [RW] Output Level [Sound Mode #3] | |
| Bit6-5 Output Level: | |
| 00: MUTE 01: 100% 10: 50% 11: 25% | |
| ------------------------------------------------------------------------------ | |
| FF1D -- SNDREG33 [W] Frequency Low [Sound Mode #3] | |
| Lower 8 bits of the 11bit frequency. Higher 3 bits are in SNDREG34. | |
| ------------------------------------------------------------------------------ | |
| FF1E -- SNDREG34 [RW] Frequency High [Sound Mode #3] | |
| Bit7 When 1 is written into this bit, sound restarts | |
| Bit6 Counter/Consecutive selection [only this bit can be read] | |
| Bit2-0 Higher 3 bits of the 11bit frequency | |
| ------------------------------------------------------------------------------ | |
| FF20 -- SNDREG41 [RW] Sound Length/Pattern Duty [Sound Mode #4] | |
| Bit5-0 Length of sound data | |
| ------------------------------------------------------------------------------ | |
| FF21 -- SNDREG42 [RW] Control [Sound Mode #4] | |
| Bit7-4 Initial value of envelope | |
| Bit3 Envelope up[1]/down[0] | |
| Bit2-0 Number of envelope step | |
| ------------------------------------------------------------------------------ | |
| FF22 -- SNDREG43 [RW] Polynomial Counter [Sound Mode #4] | |
| Bit7-4 Shift clock frequency for the counter | |
| 0000: Dividing ratio of frequencies / 2 | |
| 0001: Dividing ratio of frequencies / 2^2 | |
| 0010: Dividing ratio of frequencies / 2^3 | |
| .... .... | |
| 1101: Dividing ratio of frequencies / 2^14 | |
| 1100: Prohibited | |
| 1111: Prohibited | |
| Bit3 Number of steps: 7 [1]/15 [0] | |
| Bit2-0 Dividing ratio of frequences | |
| 000: f*2 010: f/2 100: f/4 110: f/6 where f = 4.194304Mhz/8 | |
| 001: f*1 011: f/3 101: f/5 111: f/7 | |
| ------------------------------------------------------------------------------ | |
| FF23 -- SNDREG44 [RW] Frequency High [Sound Mode #4] | |
| Bit7 When 1 is written into this bit, sound restarts | |
| Bit6 Counter/Consecutive selection [only this bit can be read] | |
| ------------------------------------------------------------------------------ | |
| FF24 -- SNDREG50 [RW] Channel and Volume Control | |
| Bit7 Vin -> SO2 on[1]/off[0] | |
| Bit6-4 Volume on SO2 | |
| Bit3 Vin -> SO1 on[1]/off[0] | |
| Bit2-0 Volume on SO1 | |
| ------------------------------------------------------------------------------ | |
| FF25 -- SNDREG51 [RW] Sound Output Terminal Selector | |
| Bit7 Sound 4 -> SO2 | | |
| Bit6 Sound 3 -> SO2 | | |
| Bit5 Sound 2 -> SO2 | SO1 and SO2 are two sound outputs connected to the | |
| Bit4 Sound 1 -> SO2 | headphones. Vin is an input terminal in the cartridge | |
| Bit3 Sound 4 -> SO1 | slot. | |
| Bit2 Sound 3 -> SO1 | | |
| Bit1 Sound 2 -> SO1 | | |
| Bit0 Sound 1 -> SO1 | | |
| ----------------------+------------------------------------------------------- | |
| FF26 -- SNDREG52 [RW] Sound ON/OFF | |
| Bit7 All sound on[1]/off[0] | |
| Bit3 Sound 4 on[1]/off[0] | |
| Bit2 Sound 3 on[1]/off[0] | |
| Bit1 Sound 2 on[1]/off[0] | |
| Bit0 Sound 1 on[1]/off[0] | |
| ----------------------------------------------+---------------+--------------- | |
| FF40 -- LCDCONT [RW] LCD Control | when set to 1 | when set to 0 | |
| Bit7 LCD operation | ON | OFF | |
| Bit6 Window Tile Table address | 9C00-9FFF | 9800-9BFF | |
| Bit5 Window display | ON | OFF | |
| Bit4 Tile Pattern Table address | 8000-8FFF | 8800-97FF | |
| Bit3 Background Tile Table address | 9C00-9FFF | 9800-9BFF | |
| Bit2 Sprite size | 8x16 | 8x8 | |
| Bit1 Color #0 transparency in the window | SOLID | TRANSPARENT | |
| Bit0 Background display | ON | OFF | |
| ----------------------------------------------+---------------+--------------- | |
| FF41 -- LCDSTAT [RW] LCD Status | when set to 1 | when set to 0 | |
| Bit6 Interrupt on scanline coincidence | ON | OFF | |
| Bit5 Interrupt on controller mode 10 | ON | OFF | |
| Bit4 Interrupt on controller mode 01 | ON | OFF | |
| Bit3 Interrupt on controller mode 00 | ON | OFF | |
| Bit2 Scanline coincidence flag | COINCIDENCE | NO COINCIDENCE | |
| Bit1-0 LCD Controller mode: | |
| 00 - Horizontal blanking impulse [VRAM 8000-9FFF can be accessed by CPU] | |
| 01 - Vertical blanking impulse [VRAM 8000-9FFF can be accessed by CPU] | |
| 10 - OAM FE00-FE90 is accessed by LCD controller | |
| 11 - Both OAM FE00-FE90 and VRAM 8000-9FFF are accessed by LCD controller | |
| ------------------------------------------------------------------------------ | |
| FF42 -- SCROLLY [RW] Background Vertical Scrolling | |
| ------------------------------------------------------------------------------ | |
| FF43 -- SCROLLX [RW] Background Horizontal Scrolling | |
| ------------------------------------------------------------------------------ | |
| FF44 -- CURLINE [RW] Current Scanline | |
| This register contains the number of a screen line currently being | |
| scanned. It can take values 0-153 where 144-153 indicate the vertical | |
| blanking period. Writing into this register resets it. | |
| ------------------------------------------------------------------------------ | |
| FF45 -- CMPLINE [RW] Scanline Comparison | |
| When contents of CURLINE are equal to contents of CMPLINE, scanline | |
| coincidence flag is set in the LCD status register and an interrupt | |
| may occur. | |
| ------------------------------------------------------------------------------ | |
| FF47 -- BGRDPAL [W] Background Palette | |
| Bit7-6 Palette for color #3 | | |
| Bit5-4 Palette for color #2 | 00 ------- 01 ------- 10 -------> 11 | |
| Bit3-2 Palette for color #1 | lightest darkest | |
| Bit1-0 Palette for color #0 | | |
| ------------------------------+----------------------------------------------- | |
| FF48 -- OBJ0PAL [W] Sprite Palette #0 | |
| Bit7-6 Palette for color #3 | | |
| Bit5-4 Palette for color #2 | 00 ------- 01 ------- 10 -------> 11 | |
| Bit3-2 Palette for color #1 | lightest darkest | |
| Bit1-0 Palette for color #0 | | |
| ------------------------------+----------------------------------------------- | |
| FF49 -- OBJ1PAL [W] Sprite Palette #1 | |
| Bit7-6 Palette for color #3 | | |
| Bit5-4 Palette for color #2 | 00 ------- 01 ------- 10 -------> 11 | |
| Bit3-2 Palette for color #1 | lightest darkest | |
| Bit1-0 Palette for color #0 | | |
| ------------------------------+----------------------------------------------- | |
| FF4A -- WNDPOSY [RW] Window Y Position | |
| WNDPOSY may assume values 0-143. It determines the vertical position | |
| of the left upper corner of a window on the screen. | |
| ------------------------------------------------------------------------------ | |
| FF4B -- WNDPOSX [RW] Window X Position | |
| WNDPOSX may assume values 7-166. It determines the horizontal position | |
| of the left upper corner of a window on the screen. The real position | |
| is WNDPOSX-7. | |
| ------------------------------------------------------------------------------ | |
| FF46 -- DMACONT [W] DMA Transfer Control | |
| Writing to this register will cause a DMA transfer into OAM located | |
| at FE00-FE9F. The written value determines the source address in a | |
| following way: 00 -> 0000, 01 -> 0100, ... , 9A -> 9A00, ... | |
| The DMA transfer takes about 160 nanoseconds. | |
| Example: | |
| ; Routine transferring 0400-049F into OAM | |
| DI ; Disable interrupts | |
| LD A,04h ; Transferring data from 0400h | |
| LD (FF46h),A ; Start DMA transfer | |
| LOOP: LD A,#40 ; Wait | |
| DEC A ; | |
| JR NZ,LOOP ; | |
| EI ; Enable interrupts | |
| ----------------------------------------------+---------------+--------------- | |
| FFFF -- ISWITCH [RW] Interrupt Enable/Disable | when set to 1 | when set to 0 | |
| Bit4 Transition High->Low on pins P10-P13 | ENABLED | DISABLED | |
| Bit3 End of serial I/O transfer | ENABLED | DISABLED | |
| Bit2 Timer overflow | ENABLED | DISABLED | |
| Bit1 LCD controller interrupt [see LCDSTAT] | ENABLED | DISABLED | |
| Bit0 LCD vertical blanking impulse | ENABLED | DISABLED | |
| ----------------------------------------------+---------------+--------------- | |
| © Copyright by Marat Fayzullin |
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