Re: [stella] Re: ZP,Y -> ABS,Y

Subject: Re: [stella] Re: ZP,Y -> ABS,Y
From: Christopher Tumber <christophertumber@xxxxxxxxxx>
Date: Thu, 24 Oct 2002 16:35:38 -0400
>That's not a bug, it's a feature!  DASM assumes that since the 6502 doesn't
>have a ZP,Y, that you must have meant ABS,Y.

Well, you know what they say about what happens when you assume...

It really should flag an error! If you want absolute, then put absolute. There's no real reason I can see why someone would do lda $80,y instead of lda $0080,y on purpose. If I do lda $80),y is it going to give an error or just assume lda ($80),y?

There's just too much chance that lda $80,y is a real error of some kind and not just dropping the leading zeroes. Maybe you mean't lda$80,x or maybe you just mean't lda $80 or maybe you mean't lda $f080,y. Either way, there's an error there somwhere!

I mean really, other than for timing issues, how often are you ever going to do lda $0080,y? So chances are if someone's doing lda $80,y it's a real error! (And if it's not, there's nothing wrong with making the programmer be explicit about it when otherwise there's so many potential problems.)

>I have to admit that the 6809 has a nice ISA.  I cut my teeth programming
>in assembly on the CoCo and it was quite a shock when I tried to get down &
>dirty on an Apple ][; no 16 bit index registers!  Only a single 8 bit
>accumulator!  No multiply instruction!  Aaagh!  And I nevery understood the
>Apple's hi-res graphics memory map.

I actually learned asm in high school on Apple II's (pretty much the best class ever in high school!) which translated really nicely to the Commodore 64 I had at home. To this day I'm thankfull to that teacher who took it on his own initiative to introduce asm to the class when the typical computer science class at the time (early/mid-80's) was all about brain-dead BASIC programming. I've watched enough people struggle to pick it up asm to know that was a really, really good way to learn. (And I can't imagine a computer science class teaching asm today (particularly 8 or 16 bit asm!) until well into the college/specialist level!)

So 6809 was pretty luxurious (and don't get me started on wierd-ass Intel memonics!)


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