Card Slot Check from Mabel's Mansion
(present on track $18, sector $0F)

7D00-   A2 07       LDX   #$07
7D02-   A0 00       LDY   #$00
7D04-   A9 00       LDA   #$00
7D06-   8D 00 C7    STA   $C700
7D09-   AD 00 C7    LDA   $C700
7D0C-   D0 06       BNE   $7D14
7D0E-   88          DEY
7D0F-   D0 F3       BNE   $7D04
7D11-   4C 00 C6    JMP   $C600
7D14-   CE 08 7D    DEC   $7D08
7D17-   CE 0B 7D    DEC   $7D0B
7D1A-   CA          DEX
7D1B-   D0 E5       BNE   $7D02

// For additional interest, the code continues into a loop to decode the rest of the program.
// There is another loop that runs a checksum on the code, and jumps to a reset/reboot routine if modified.
// The checksum routine is called several times from different locations.
7D1D-   A9 00       LDA   #$00
7D1F-   8D FF 7D    STA   $7DFF
7D22-   A0 FF       LDY   #$FF
7D24-   B9 FF A5    LDA   $A5FF,Y
7D27-   59 00 A6    EOR   $A600,Y
7D2A-   99 00 A6    STA   $A600,Y
7D2D-   88          DEY
7D2E-   C0 FF       CPY   #$FF
7D30-   D0 F2       BNE   $7D24
7D32-   CE 26 7D    DEC   $7D26
7D35-   CE 29 7D    DEC   $7D29
7D38-   CE 2C 7D    DEC   $7D2C
7D3B-   AD 29 7D    LDA   $7D29
7D3E-   C9 7D       CMP   #$7D
7D40-   D0 E2       BNE   $7D24
7D42-   A9 EA       LDA   #$EA
7D44-   8D 29 A4    STA   $A429
7D47-   8D 2A A4    STA   $A42A
7D4A-   4C 02 7E    JMP   $7E02

To make Mabel's Mansion playable in AppleWin, sector edit:

Track $1A, sector $19, byte 6B: change from D7 to 1E (this will decode to a RTS instruction after being XOR'd)

Track $01, sector $01, byte 6F: change from 00 to 1D (this will modify what was a JMP $7D00 to JMP $7D1D)

Both of these changes bypasses the card slot check.  Presumably this was to detect the presence of copy cards back in the day.


Hot Rod
June 2012