A86: Loading data from a "variable" address. . .
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A86: Loading data from a "variable" address. . .
I've been following this list for two or three weeks now, and found it to
extremely helpful (well. . . most of the time =) Anyways, I'm working on an
RPG similar to the original Legend of Zelda for the old NES (not quite an
"RPG", but close enough). The problem I'm having is the way the data is
stored. Since the map is split into many sections (one at a time), I have
all the data stored for them in Sections labeled Screen1, Screen2, etc. . .
So every time you move right a screem, the number is increased by one, left
decreases one, and up or down decreases or increases by the number of
screens in a row.
For example:
Screen01 Screen02 Screen03 Screen04 Screen05
Screen06 Screen07 Screen08 Screen09 Screen10
Screen11 Screen12 Screen13 Screen14 Screen15
. . . etc., etc. . .
What I want to do is have the "a" register pointing to the data. Assuming
you start in Screen01 and move down a screen, you'll be at Screen06. What I
want to do is set "b" to be equal to 6 (or, if possible, use OP1 to store
the string "Screen06"), and do something like "ld a, [the label in b/OP1]".
I've been trying to find a way to do this, and I think it may involve
_ABS_DEST_ADDR (is that absolute destination address?) and
_SET_ABS_DEST_ADDR -- but I have no clue how to use them. . .
I could also use "cp b,1 / jp z,SetAToScreen01 / cp b,2 / jp
z,SetAtoScreen02" etc. (and have those labels do just what they say), but
that's at least 2 or 3 times the memory, and not flexible enough (if I use
other labels -- like Dungeon01, or Cave02) -- so i anyone could help me, I'd
appreciate it. . .
And, does anyone have any clue how the Zelda enemy AI works? I was watching
the game; half of what the guys did was completely random (Firing in the
opposite direction from me, moving straight random amounts of time before
turning), and half was actually moving TOWARDS me and aiming AT me (not an
easy feat -- I've got a few ideas as to how I'll program them, but They may
be pretty dumb =) I got the Gameboy Zelda ROM image and decompiled it, but
It's impossible to find ANYTHING in 120K of decompiled Z80 source code --
and it's only legal to have these things 24 hours without owning the actual
game. . .
I've also got a few other ASM questions:
1) When do I need to use "ret", and when don't I??? I've seen source code
for some programs that jump, do a routine, and go back but don't use
"ret" -- When does it know to return?
2) I've seen cases where "call" was used exactly like "jp" -- and NOT for
ROM calls?!? Am I allowed to use it for anything else???
3) While I'm at it, is a TI-89 list going to open soon?
4) Since the 89 will use a Motorola 68000 like the TI-92, the assembly will
be like Fargo, not the 82, 83, 85, 86, or any of the others that use a 6MHz
Z80, right? If so, does anyone here know of a good Fargo reference source?
(again, it's the wrong list, but I'm not on the TI-92 list and this is more
convenient).
Anyways, that's enough for one E-Mail -- I'd appreciate any help I can get.
Thanks!
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