Slot 2 Mapping

The v0 ROM contains a bug which is fixed in v1:

v0 awards the player 100 points for breaking any window; v1 only awards points for breaking the window of a non-subscriber. The latter rules match those of the original arcade version.

The following code is executed when a newspaper breaks a house window:


 3138: CD 13 4B     CALL 4B13h


 3138: CB 46        BIT 0,(HL)
 313A: CC 15 4B     CALL Z,4B15h

Here, HL points to information about the house - bit 0 is 0 for a non-subscriber and 1 for a subscriber. Only the v1 ROM tests this bit before calling the function to increase the player's score.

There is at least one other difference between the ROMs. The following code is present in v1 but not in v0:

 5997: 78           LD A,B
 5998: A7           AND A
 5999: 20 0F        JR NZ,+0Fh (59AAh)
 599B: FD 21 18 CA  LD IY,CA18h
 599F: FD 7E 0A     LD A,(IY+0Ah)
 59A2: FE 0C        CP 0Ch
 59A4: 20 04        JR NZ,+04h (59AAh)
 59A6: FD 21 80 D0  LD IY,D080h

The exact purpose of this additional code is unknown.

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