*** C128 Auto-boot sector layout
*** Document revision: 1.1
*** Last updated: March 11, 2004
*** 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?????????????
0010: 5F FF A9 05 8D 06 D5 A9 4E 8D 00 FF 4C 00 0C 00  _???????N???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.