Hi guys!

I've started coding some routines. For my homebrew but I'm still getting stuck on some of the addressing types.

The problem I am experiencing is when I try to store a value at a particular memory address.

Attempting to store 'FF' at location $0002 works for me by doing this;


But doesn't work if I do this;


Any idea why the latter doesn't work? (Or should it?)

Many thanks in advance!

Gah, just realised I am storing at the location pointed to in $0002 for the first example (which is actually what I wanted). Noob mistake.

Is there any way to to do an STA($02,x) without having to have the offset x?

A 65C02 can simply:



-Gordon

_________________
--
Gordon Henderson.
See my Ruby 6502 and 65816 SBC projects here: https://projects.drogon.net/ruby/

Awesome, good to know. The IDE I am using only knows about the 6502. I'll have to see if there is a way the instruction set can be extended.

I guess I could look up the opcode and put the hex codes inline at worst.

Thanks again!

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Will certainly look at doing that

Thanks guys! 0x92 sta(zpg) worked well.

Currently writing an emulator for my hardware. I am using the mos6502 framework here - https://github.com/gianlucag/mos6502

Unfortunately it only supports 6502 and not W65C02. But I managed to wrangle the 0x92 opcode to it and it seems to be performing as intended. So all is going well.

I might look at adding the other W65C02 opcodes to it at a later date.

Many thanks once again. You guys are legendary!

Sounds like good progress!

Hang about!

Why did:

STA $02

Not work?

_________________
Bill

STA $02 did work, but didn't do what he actually wanted, which was indirect addressing.

Ahh, okay. To what advantage? I'm still missing something, but in my defense I'm not one of the worlds better known 65(C)02 code hounds.

_________________
Bill

He was after using $02 and $03 as a 16-bit pointer to a memory location - the low byte stored in $02 and the high byte in $03. In 65C02 land you can simply



in non C land, then you need to use an index register (set to zero for this case).

-Gordon

_________________
--
Gordon Henderson.
See my Ruby 6502 and 65816 SBC projects here: https://projects.drogon.net/ruby/

In NMOS-ville, you can also leave the LSB of the pointer in memory zeroed, load the real LSB in Y, and do STA ($02),Y instead.

...and also never pay an extra cycle for crossing a page boundary.

BTW, for an NMOS 6502, you can store (or load) a value at the address pointed to by a lo/hi pointer in zero page by either:



(which may actually be the most common use of the rarely-used pre-indexed indirect address mode)

or



But if you don't want to mess with the index registers at all, you'll need to use a CMOS 6502.

Actually, some of us rely quite heavily on the pre-indexed indirect mode, and find it to be a real boon! But on an NMOS 65xx I can also see the case for using it with X=0.

Or Self Modifying Code (which can simulate all sorts of novel and useful address modes). Garth wrote about that and oiher aspects of SMC here.

-- Jeff

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html