Illegal opcode usefull?

[Heaven/TQA]

just went through several lists of illegal opcodes for the atari800...

 

anybody using them? i mean f.e. LAX is straight forwared and understandable but for what are the rest usefull??? anybody has some examples where they might be a step forward in terms of quicker or less bytes used?

[Thomas Jentzsch]

i mean f.e. LAX is straight forwared and understandable but for what are the rest usefull??? anybody has some examples where they might be a step forward in terms of quicker or less bytes used?

Check the [stella] mailing list!

[Heaven/TQA]

http://www.biglist.com/lists/stella/archiv...6/msg00061.html

 

hehehe... just found it... DCP is mentioned in my docs like DEC... you mention it in your post with DEC and CMP... so... what is DCP?

[Thomas Jentzsch]

http://www.biglist.com/lists/stella/archives/200006/msg00061.html

And many more.

 

DCP is mentioned in my docs like DEC... you mention it in your post with DEC and CMP... so... what is DCP?

DEC

CMP

[Aaron]

One of the nice things about, e.g. DCP is that it supports address modes that DEC does not. DEC (foo),y is impossible but DCP (foo),y works fine, so it can be a quicker way of decrementing something if you don't care about the flags.

 

LAX works like this too - LDX (foo),y doesn't exist but LAX (foo),y does.

 

And of course there are times when you actually want to increment something and then subract it from A (ISB), but those are rare... :wink:

 

Anyway, you said you went through several lists, but this one is my favorite: http://atarihq.com/danb/files/64doc.txt, even if the explanations are a little cryptic...