Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utgpu!water!watmath!clyde!rutgers!husc6!cmcl2!yale!xwallman From: xwallman@yale.UUCP Newsgroups: comp.sys.atari.st Subject: Re: SPECTRUM 512 how do they do it ? Message-ID: <19278@yale-celray.yale.UUCP> Date: Fri, 20-Nov-87 18:24:21 EST Article-I.D.: yale-cel.19278 Posted: Fri Nov 20 18:24:21 1987 Date-Received: Sun, 22-Nov-87 12:31:26 EST Sender: root@yale.UUCP Reply-To: xwallman@gator.UUCP (Natuerlich!) Organization: Yale University Computer Science Dept, New Haven CT Lines: 46 How they do it ? I don't know. What's my guess, given the constraints of the hardware (and there isn't much in there except some RAM, a 68000 and the SHIFTER) ? Allright usually on my old and beloved 800 everyone used DLIs (now in ST-Talk that's called HBLs) for multiple colors. An interrupt occured after (*) a scanline. And one had the time to change color registers, in perfect synch with the display. But this really isn't neccessary. You don't have to switch colors on scanlines. You can switch them anytime you wan't. (True for ST and 800) Problem is that you need to get the CPU somehow in sync, with the display. This was impossible (?(*)) if you have a co-processor stealing cycles (as ANTIC does) but the SHIFTER doesn't and this makes things easier for the ST. From previous postings (I have never seen the actual product, much less a picture) I read that only 199 lines can be shown with SPECTRUM 512. My guess is that the first DLI (Ooops HBL) is used for starting synchronization. Then the CPU will spring into action, kerchunking away, changing registers on the fly. Here is where above mentiones RAM comes into the picture. Displays with 300/200/9? Bits are BIG. So I think this is a theory that would work in praxis, I would be very surprised if SPECTRUM 512 wouldn't work that way. (Surprise me !) (*) Not really after, somewhere in the middle of the scanline. (**) Footnote : I managed once to get a somewhat appealing display giving the ANTIC some cycles, but usually it's just a mess. Out-of-YALE-callers please use only these addresses <<<>>>> <.......................IIII, ..< <......III, ..........IXI, .....< <.....IXIIXI, ......IXI,, ......< <....IXI,,IXI, ...IXI,, ........< <...IXI,, .IXI, IXXI,, .........< <..IXXI,, ..IXXXXXI,, ..........< <.IXXI,, ....IXXXI,, ...........< >>>>>>>> And grand new opening at WALLMANN@CTSTATEU.BITNET (yale addresses preferred)