Noob question about forcing an addressing mode

[TROGDOR]

Atari Gurus,

 

I'm in the middle of writing a very hairy 2-line kernel, and I've come across an instance where I need to force a zero-page STA to take 4 cycles. I can do this by making the store absolute instead of zero-page, but is there a clean way to do this in DASM without having to specify the opcode bytes?

 

I've got:

 

STA Temp4

 

The ugly way to force this is:

 

.byte #$8D

.byte #Temp4

.byte #$00

 

Correct?

 

Thanks,

Edited January 20, 2006 by TROGDOR

[Tom]

sta.w Temp4

[TROGDOR]

Thanks Tom.

[Zach]

If you need four cycles, indexed addressing also works when X or Y is constant, plus it's only 2 bytes whereas STA.w is 3. For example if X=#$10, then STA Temp4-16,X would be your code.

Edited January 20, 2006 by Zach

[Bruce Tomlin]

It all depends on what your assembler lets you do. "sta.w" is a DASM-ism. Other assemblers might use a strategically placed ">" character.

 

But on a 2600, you can take advanage of the incomplete address decoding and force extended addressing mode by using $01xx: "STA Temp4+$100"