Re: A86: Loading data from a "variable" address. . .
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Re: A86: Loading data from a "variable" address. . .
Scott Noveck (SMN) wrote:
>
> 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. . .
Here's what you need to do:
ld hl,string6
rst 20h ;op1 has the sting
string6:
.db "Screen06",0
I'm not sure what you want to do with it from there... If I were you, I
would use a hex number to represent each screen, set up a data table
with each of the of the strings in order, and then multiply your hex #
by 9 to get the string (each string is 9 characters) when you need to
display it. If a contains the hex # and ix points the start of the
table:
ld h,a
ld l,9
call _mul_hl
add hl,ix
call _puts
something like that...
>
> 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?
If the instruction before the ret is a call, then jp does the same
thing:
call _puts
ret
is the same as
jp _puts
The ret at the end of the _puts call functions as your ret when you use
jp.
> 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???
You can use calls to your own code, it simply returns to the instruction
following the call after the subroutine is finished
> 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!
>
> S___________________________________________________C
> | The FIRST SimCity 3000 Site ~~ By Scott Noveck |
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> noveck@pluto.njcc.com (preferable)
> SMN@geocities.com (slower)
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