Gameboy boot Rom assembly code and comments

After the Gameboy power is turned on, a 256-byte program will be loaded to the 0 position of the memory and run. This program is left and right. Check the card with a verification code and display and scroll the logo, the following code and comments are used to play the prompts:

LD sp, $ fffe; $0000 set the stack pointer <br/> xor a; $0003 reset the $8000-$ 9fff part (Display memory) <br/> ld hl, $ 9fff; $0004 <br/> addr_0007: <br/> LD (HL-), A; $0007 <br/> bit 7, H; $0008 <br/> Jr NZ, addr_0007; $ 000a <br/> ld hl, $ ff26; $ 000c set audio <br/> ld c, $11; $ 000f <br/> ld a, $80; $0011 <br/> LD (HL-), A; $0013 <br/> LD ($ ff00 + C), a; $0014 <br/> Inc C; $0015 <br/> ld a, $ F3; $0016 <br/> LD ($ ff00 + C), a; $0018 <br/> LD (HL -), a; $0019 <br/> ld a, $77; $ 001a <br/> LD (HL), A; $ 001c <br/> ld a, $ FC; $ 001d set the background palette <br/> LD ($ ff00 + $47), A; $ 001f <br/> LD de, $0104; $0021 convert the logo from the cassette and load it into the video memory <br/> ld hl, $8010; $0024 <br/> addr_0027: <br/> lD, (DE); $0027 <br/> call $0095; $0028 <br/> call $0096; $ 002b <br/> Inc de; $ 002e <br/> ld a, E; $ 002f <br/> CP $34; $0030 <br/> Jr NZ, addr_0027; $0032 <br/> LD de, $00d8; $0034 load the attached 8 bytes to the video memory <br/> ld B, $08; $0037 <br/> addr_0039: <br/> ld a, (de); $0039 <br/> Inc de; $ 003a <br/> LD (HL +),; $ 003b <br/> Inc HL; $ 003c <br/> dec B; $ 003d <br/> Jr NZ, addr_0039; $ 003e <br/> lD, $19; $0040 set the background tilemap <br/> LD ($9910), A; $0042 <br/> ld hl, $ 992f; $0045 <br/> addr_0048: <br/> ld c, $ 0C; $0048 <br/> addr_004a: <br/> dec A; $ 004a <br/> Jr Z, addr_0055; $ 004b <br/> LD (HL-), A; $ 004d <br/> dec c; $ 004e <br/> Jr NZ, addr_004a; $ 004f <br/> ld l, $ 0f; $0051 <br/> Jr addr_0048; $0053 <br/>; === scroll the logo on the screen and play a logo sound ===< br/> addr_0055: <br/> ld h, A; $0055 load the scroll count, H = 0 <br/> ld a, $64; $0056 <br/> ld d, a; $0058 set the cyclic count, D = $64 <br/> LD ($ ff00 + $42), a; $0059 set the horizontal scroll register <br/> ld a, $91; $ 005b <br/> LD ($ ff00 + $40), a; $ 005d enable LCD, display background <br/> Inc B; $ 005f <br/> addr_0060: <br/> ld e, $02; $0060 <br/> addr_0062: <br/> ld c, $ 0C; $0062 <br/> addr_0064: <br/> ld a, ($ ff00 + $44); $0064 waiting for screen seek <br/> CP $90; $0066 <br/> Jr NZ, addr_0064; $0068 <br/> dec c; $ 006a <br/> Jr NZ, addr_0064; $ 006b <br/> dec E; $ 006d <br/> Jr NZ, addr_0062; $ 006e <br/> ld c, $13; $0070 <br/> Inc h; $0072 auto-increment rolling count <br/> ld a, h; $0073 <br/> ld e, $83; $0074 <br/> CP $62; $0076 playback sound #1 after 62 times <br/> Jr Z, addr_0080; $0078 <br/> ld e, $ C1; $ 007a <br/> CP $64; $ 007c <br/> Jr NZ, addr_0086; $ 007e: After 64 times of counting, the playing sound # <br/> addr_0080: <br/> ld a, E; $0080 play sound <br/> LD ($ ff00 + C), a; $0081 <br/> Inc C; $0082 <br/> ld a, $87; $0083 <br/> LD ($ ff00 + C), a; $0085 <br/> addr_0086: <br/> ld a, ($ ff00 + $42 ); $0086 <br/> sub B; $0088 <br/> LD ($ ff00 + $42),; $0089 if B = 1, scroll up <br/> dec D; $ 008b <br/> Jr NZ, addr_0060; $ 008c <br/> dec B; $ 008e auto-minus B <br/> Jr NZ, addr_00e0; $ 008f... jump to "Nintendo logo check" <br/> ld d, $20; $0091 use a rolling loop to suspend <br/> Jr addr_0060; $0093 <br/>; ==== image part ===< br/> ld c, A; $0095 convert image data and store it in the video memory <br/> ld B, $04; $0096 <br/> addr_0098: <br/> push BC; $0098 <br/> rl c; $0099 <br/> RLA; $ 009b <br/> pop BC; $ 009c <br/> rl c; $ 009d <br/> RLA; $ 009f <br/> dec B; $00a0 <br/> Jr NZ, addr_0098; $00a1 <br/> LD (HL +), A; $00a3 <br/> Inc HL; $00a4 <br/> LD (HL +), A; $00a5 <br/> Inc HL; $00a6 <br/> ret; $00a7 <br/> addr_00a8: <br/>; Nintendo logo <br/>. DB $ ce, $ ed, $66, $66, $ CC, $ 0d, $00, $ 0b, $03, $73, $00, $83, $00, $ 0C, $00, $ 0d <br/>. DB $00, $08, $11, $ 1f, $88, $89, $00, $ 0e, $ DC, $ CC, $ 6e, $ E6, $ DD, $ DD, $ D9, $99 <br/>. DB $ BB, $ BB, $67, $63, $ 6e, $ 0e, $ EC, $ CC, $ DD, $ DC, $99, $ 9f, $ BB, $ B9, $33, $ 3E <br/> addr_00d8: <br/>; additional 8-byte data <br/>. DB $ 3c, $42, $ B9, $ A5, $ B9, $ A5, $42, $ 3C <br/>; ===== Nintendo logo comparison section =====< br/> addr_00e0: <br/> ld hl, $0104; $00e0; hl points to the Nintendo logo on the card <br/> LD de, $00a8; $00e3; de points to the Nintendo logo in DMG Rom <br/> addr_00e6: <br/> ld a, (de); $00e6 <br/> Inc de; $00e7 <br/> CP (HL); $00e8; compare the logo data on the card and DMG Rom <br/> Jr NZ, $ Fe; $00e9; if not, lock it here <br/> Inc HL; $ 00eb <br/> ld a, L; $ 00ec <br/> CP $34; $ 00ed; a total of $30 checks <br/> Jr NZ, addr_00e6; $ 00ef <br/> ld B, $19; $00f1 <br/> lD a, B; $00f3 <br/> addr_00f4: <br/> Add (HL ); $00f4 <br/> Inc HL; $00f5 <br/> dec B; $00f6 <br/> Jr NZ, addr_00f4; $00f7 <br/> Add (HL ); $00f9 <br/> Jr NZ, $ Fe; $ 00fa; if the sum of all the bytes from $0134 to $ 014d plus $19 is not 0, lock <br/> ld a, $01; $ 00fc <br/> LD ($ ff00 + $50), a; $ 00fe; Disable DMG Rom