Subject: Re: [stella] Hardware comparisons From: "Peter Pachla" <peter.pachla@xxxxxxxxxxxxxxxxx> Date: Thu, 27 Apr 2000 17:52:24 +0100 |
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 -- -- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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