Hi Clay,
>> OK ANTIC *IS* a CPU, albeit one with a very simple instruction set....
>
> Actually ANTIC is a coprocessor....
I think we're arguing about semantics here.
It's being USED as a graphics co-processor, but it is a very simple
processor in it's own right.
>....A system can only have one *central* processing unit, after all.
Again, we're heading down a slippery slope here.
It depends on how you define "CPU". The CPU in simple systems may consist of
a single (micro)processor, in more complex systems (like IBM RS/6000 systems
for example) the CPU may be composed of several individual processor units.
I think the problem is that I, like most people, tend to use the word "CPU"
when I actually mean "microprocessor", IYSWIM?
>> AFAIR, without intervention from the 6502, all ANTIC can change on a
>>scanline by scanline basis is the display mode.
>
> ANTIC can also change where display data is being fetched from....
Errm, AFAIR that is defined by the instructions in the display list along
with the contents of the HSCROL/VSCROL registers. ANTIC cannot change these
itself.
>....where display list data is fetched from....
But that is controlled by the DLISTH/L registers. Again I don't know of any
way ANTIC can alter this register itself.
Yes, you can perform "jump" instructions within the display list but these
only allow you to jump over a 1K boundary and to jump back to the start of
the "program".
>....and insert blank lines.
OK, but I've always considered those display modes - just ones which happen
to output from 1 to 8 blank lines.
> You mean "coarse scroll". A hard scroll is in fact physically moving
display
>data around.
True, again I'm guilty of using the terms interchangeably all too often....
TTFN - Pete.
--
Hardware & Software Engineer. Sound Engineer.
Collector of Arcade Machines, Games Consoles & Obsolete Computers (esp DEC)
peter.pachla@xxxxxxxxxxxxxxxxx | www.wintermute.org.uk
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