Pc-98 Bios (Official × 2026)

AH = 17h AL = rate (0–3Fh) INT 18h Set cursor position

AH = 10h INT 18h Returns: AL = ASCII, AH = scancode

AH = 63h CX:DX = microseconds INT 18h (blocks) Get BIOS version

AH = 42h (same registers as read)

AH = 21h DH = row (0–24 or 0–27) DL = column (0–79) INT 18h

AH = 25h AL = lines to scroll CH = top row, CL = left col DH = bottom row, DL = right col BH = fill color INT 18h

msg db 'Hello from PC-98 BIOS!', 0

AH = 70h INT 18h Returns: AX = BCD version (e.g., 0x0123 = v1.23)

AH = 11h INT 18h ZF = 1 if no key ZF = 0 if key waiting → AX = scancode/ASCII

AH = 62h CX:DX = microseconds between interrupts INT 18h pc-98 bios

; NASM syntax, PC-98 target ORG 100h start: mov ah, 24h ; write character mov bh, 7 ; gray on black mov si, msg .loop: lodsb test al, al jz done mov al, al int 18h jmp .loop done: ret

AH = 72h INT 18h Returns: AX = bitmask (FDD count, display type, etc.) BIOS is slow but safe. For games/demos, bypass BIOS and access hardware directly. Common direct I/O ports (simplified): | Port | Purpose | |------|---------| | 0x60 | Keyboard data | | 0x61 | Keyboard control | | 0x66 | Display controller (GDC) | | 0x68 | CRTC address | | 0x6A | CRTC data | | 0xA0 | FDC status | | 0xA1 | FDC data | | 0x30 – 0x3F | Sound (YM2203/2608) | | 0x64 | Timer / interrupt mask |

AH = 45h DL = drive Returns: BL = sectors per track, BH = heads Get system timer ticks AH = 17h AL = rate (0–3Fh) INT

AH = 22h Returns: DH = row, DL = column

AH = 41h DL = drive CX = track number (0–79 for 2HD) DH = head (0 or 1) CH = sector number (1–8 for 2HD) AL = number of sectors ES:BX = buffer INT 18h Returns: CF = 0 if OK