Some "inside" informations...
Subject: PM-transparency etc. Szia Karesz, Yesterday I've checked the
PM-transparency problem; Actually I wasn't correct when I wrote to you
about this last year. Unfortunately the thing looks not so good; only the
four missiles can be made transparent on a Gr.9 screen, and only if the
GPRIOR register is set up as follows: - set GTIA mode to Gr.9 (bit 6=1,
bit 7=0) - set priority to 0 (bits 0-3 = 0) - set 5th player mode for missiles
(bit 4=1) so GPRIOR has to be set to $50. Then the color of the overlapping
area will be: color of missiles ($d019/$02c7) logical-ORed with color of
background ($d01a/$02c8). I'm not 100% sure about the truth of the last
sentence, but this was my impression. I investigated these PM priority
modes a couple of years ago, but I forgot to write down anywhere - the
same as for the HIP effect ;-) Anyway, I have some older routines that
I wrote in Atmas II, which make use of this effect, so I'll check them
out again, and make a small doc about it. But you can also check it yourself.
BTW, I've also got Atari Intern, and it is one of my primary sources about
the Atari... It has the most comprehensive description of the Atari hardware,
which I have (I don't have the Atari Hardware Manual). Of course (?), even
Atari Intern does not describe things like this priority-0/PM-transparency.
(to say nothing of HIP, for example) But doesn't matter, we have left with
enough new things to explore. ;-) BTW, we should collect all the undocumented
features of Atari in a document, (that is, make them *documented* ;-) )
and put it online on a web page to allow everybody to profit from them.
What's your opinion? As for the illegal opcodes on your page, I also have
a couple of other docs describing these. There are some differences in
the description of some of the opcodes, especially for the more complicated
ones - probably because they can do really unpredictable things. (Known
only for those, who know the inner workings of the 6502.) When I wrote
MoniTOM, my monitor program back in 1992, I investigated most of these
instructions, and included them in both the assembler and disassembler
part of the program. (So you can use all the 256 instructions with it!)
Now, that I'm redesigning MoniTOM, have another chance to clear this topic
up - I plan to make redefinable even the mnemonic names of the opcodes
by a config program - this can be useful because the same opcode is mentioned
on 3-4 different names in different sources. To tell the truth, I've used
only a couple of these instructions so far. Mostly in the boot blocks of
Veronika and CE. But never in effects. I know, Sanyi used the LAX ($xx),Y
instruction in the landscape routine in Joyride. (This is why it won't
run on the 65816 turbo cards... ;-) ) Do you know where I can find this
APE-debugger you wrote about? Because I can't find anywhere. I'd be really
interested in it as you can bet... ;-) Have you managed to depack the mails?
OK, that's all for now. Udv, Tamas
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Tamas Bene ---
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/ / /_|_ | |__\ Software, Hungary
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Last changes: 18 maj 1998
Feel free to contact me for any legal reason!
HeAvEn, Member of TaquarT