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

CPU test
ROM checksum
DMA controller
Timer
Memory test
Keyboard init
Video init
Extension ROMs
Equipment check
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.