>
> In Haunted House, the problem you describe occurs at address
> $F441 where
> this opcode is executed: SBC $0F. Reading from $0F has an
> undefined result,
> a real atari 2600 will read, and subtract to the accum, #$0F.
> This happens
> because, since the read can´t be done, the data bus isn´t updated, so
> whatever the bus has on the previous cicle will be used. Reading other
> values instead of #$0F causes problems with the position of
> the player, in
> particular if #$00 is read, the game will enter into an endless loop.
>
>\
I still remeber when I discovered this when writing my 2600 emulator many
years ago. Has anyone ever looked at that section of code to see why SBC $0F
is used? Did the programmer do this knowing it would return #$0F or was this
an error of some sort?
Dan
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