Re: [stella] Brick wall ahead

Subject: Re: [stella] Brick wall ahead
From: doppel <gentlben@xxxxxxxxxxxx>
Date: Sun, 24 Oct 1999 19:03:12 -0700
> Noo, noo, noo, you don't control the zero flag, instructions set it.  > Any arithmetic operation as well as any load (LDA, LDX, LDY) simply  
> sets the zero flag if the result of the operation or the value loaded 
> is zero or clears the zero flag if the result is nonzero.

also, if you do a compare, like this: 

LDA memorylocation1
CMP memorylocation2

the zero flag will be set if both memory locations are equal.  it will
be cleared if they are greater or less that case other flags
are set ;)

> >Or do I pull the byte for the
> >flags into A, AND it to turn off the zero flag bit,
> >and STA it back in RAM?

why don't you just load A with zero, like this: LDA #$00
the only way you can be sure of turning off the zero flag bit is
by doing an AND #$00...i hardly see the point.
> Methinks someone should've had a bit more assembly language experience
> before diving headlong into the 2600.. that sentence makes very little
> sense :)

hey, i had ZERO experience with it before i began dabbling with the 
2600, and now i feel quite confident about doing things with the 6502
assembly language that i never dreamed of :) some things are better
learned "hands-on", i think.


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