Posted By
johnnnyG
on 2018-05-19
11:40:53
|  Learning 6502 assembly
I've been learning 6502 assembly using cbm prog studio and reading a book by Butterfield and Richard Mansfield. Both books discuss how one can use indirect addressing to get data from a table (like messages), but there isn't an example. Could someone provide me one please? I don't care what method is used.
|
|
Posted By
Csabo
on 2018-05-19
15:30:56
| Re: Learning 6502 assembly
Sure. I think you mean the "Indirect Indexed" mode. Here's an example:
Let's say there's some data you want to read from $1200. We will put this 16 bit address to $D0 (which is just an arbitrary, but commonly used zeropage address). Then, we will read the 1st byte from there.
LDA #$00
STA $D0
LDA #$12
STA $D1 ; now $D0/$D1 "points to" $1200
LDY #$00
LDA ($D0),Y ; this is the indexed indirect mode. So, this will take whatever 2 byte/16 bit address $D0/$D1 points to ($1200 in this case, since we just set it above), then index it with Y. Therefore, this is equivalent of LDA $1200.
INY
LDA ($D0),Y ; similarly, this will read from $1201 in this case.
As you can see, since the value of $D0/$D1 can be easily changed, you can have the same routine process different memory areas. That's it in a nutshell. Are you trying to code something specific?
|
|
Posted By
johnnnyG
on 2018-05-19
16:06:02
| Re: Learning 6502 assembly
that helps. I'm not coding anything specific. Just trying to learn. thanks
|
|
Posted By
Andras78
on 2018-05-28
02:36:42
| Re: Learning 6502 assembly
dear Gurus. I'm looking for a method to disassembly a loaded PRG and found the data storage, for example: where are the Text data of the screen text (at the current running phase).
I use VICE monitor, but there is a method to gain these result to an Editor (in text format)?
Or other disassembly tool?
thank you in advance. Andras
|
|
Posted By
KiCHY
on 2018-05-28
02:49:23
| Re: Learning 6502 assembly
My fav is Regenerator:
https://csdb.dk/release/?id=149429
|
|
Posted By
Andras78
on 2018-05-28
03:12:08
| Re: Learning 6502 assembly
this is Great, this is what I need!!
Thanks a lot!
|
|
|
|
