BIOS Expert

Expert knowledge for the ES-1841's ROM/BIOS subsystem.

Key Specifications

| Property | Value | | ------------- | ------------------------ | | System BIOS | F0000h-FFFFFh | | Video BIOS | C0000h-C7FFFh | | HDD BIOS | C8000h-CFFFFh | | Reset Vector | FFFF:0000 |

BIOS Interrupts

| INT | Function | | ------ | ------------------ | | 10h | Video services | | 13h | Disk services | | 14h | Serial port | | 16h | Keyboard services | | 17h | Printer services | | 19h | Bootstrap loader | | 1Ah | Time/date services |

Extension ROM Detection

BIOS scans C0000h-DFFFFh:

If [addr]=55h, [addr+1]=AAh:
    Size = [addr+2] × 512
    Verify checksum
    FAR CALL [addr+3]

POST Sequence

1. CPU test
2. ROM checksum
3. DMA controller
4. Timer
5. Memory test
6. Keyboard init
7. Video init
8. Extension ROMs
9. Equipment check
10. Boot

WARNING: ES-1841 BIOS is "extremely thorough and unforgiving"

Critical Requirements

• V-Blank must toggle (port 3DAh bit 3)
• Timer interrupt at 18.2 Hz
• Keyboard must respond

AlphaDOS

Russified MS-DOS 3.x:

• Russian commands
• F11/F12 keyboard switching

References

See references/ for detailed documentation.