> Cool... where do I buy one? :)
Not done yet...
> There is not a common startup address, but there is a startup vector at
> $FFFC - on powerup, the 6507's PC is set to the word stored at locations
> $FFFC and $FFFD.
Is the vector stored in the lo, hi format the same as in a jmp?(from a
quick search through existing roms, it seems so) If so, how about having a
rom like this:(system relative addresses, not rom relative)
$1000 - $1FFA = EA (nop)
$1FFB = 4C (first part of a jmp, i think)
$1FFC = FB (startup vector lo)(shouldn't actually be used)
$1FFD = 1F (startup vector hi)(shouldn't actually be used)
Assuming that I have hardware that switches from this rom to the new game
after the address $1FFB appears and the ROM becomes deselected($0XXX)(i.e.
after the 4C was loaded into the 6507). If I hot-swapped into the rom
above(swapped in the middle of a games execution), would the system start
up with the new game?
I would think that the processor would proceed to execute nops until it
got to $1FFB, where it would start a jmp, and then load the vector from
the new game.
Of course the screen update would be neglected, but I think that it would
be much smoother a transition than power cycling the VCS.
> Try experimenting with swapping in a ROM full of BRK instructions. I
> *think* the BRK instruction acts as a soft reset, resetting the PC to the
> startup vector.
Anyone else know about the BRK?
> As for wrapping around the PC... that's very unlikely to work. Within the
> 2600's address space, $1000-$1fff is ROM space, then the very next byte at
> $2000 wraps back around to $0, which is TIA input/output registers -
> trying to execute code out of those registers is unpredictable, to say the
> least. :)
oops, forgot about that.
Just curious, if the startup vector is at 1FFD:1FFC, then what is at 1FFE
and 1FFF?
Mark
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