doc:cbm:disk:c128boot
*** C128 Auto-boot sector layout
*** Document revision: 1.1
*** Last updated: March 11, 2004
*** Compiler/Editor: Peter Schepers
*** Contributors/sources: unknown
The C128 has the ability to auto-boot a floppy disk that is in the drive
when the system is powered up, but only if track 1 sector 0 contains a
specific signature. Below is a dump of an auto-boot sector with its
signature.
00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F ASCII
----------------------------------------------- ----------------
0000: 43 42 4D 00 0C 00 02 00 00 A5 D7 C9 80 F0 03 20 CBM˙˙˙˙˙˙•◊…Ä˙˙
0010: 5F FF A9 05 8D 06 D5 A9 4E 8D 00 FF 4C 00 0C 00 _˙©˙ç˙’©Nç˙˙L˙˙˙
0020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙
0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙
0040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙
0050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙
0060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙
0070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙
0080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙
0090: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙
00A0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙
00B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙
00C0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙
00D0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙
00E0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙
00F0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙˙
Bytes 00-02: Auto-boot signature 'CBM'
03-04: ???
05-06: ???
07-08: ???
09-1E: Boot code
1F-FF: ???
Below is a disassembly of the machine code contained from 09-1E.
org = $0c00
lda $d7
cmp #$80
beq skip1
jsr $ff5f
skip1 lda #$05
sta $d506
lda #$4e
sta $ff00
jmp $0c00
.end
The only document I have found which attempts to explain the layout of
the C128 boot sector doesn't fit at all for the above sector layout. I am
therefore not yet sure of all the details in the above sector. Anyone who
has more info can contact me so I can update this document.
doc/cbm/disk/c128boot.txt · Last modified: 2020/10/26 16:38 by eek