Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!cbmvax!daveh From: daveh@cbmvax.commodore.com (Dave Haynie) Newsgroups: comp.sys.amiga.hardware Subject: Re: A3000/16 Message-ID: <16318@cbmvax.commodore.com> Date: 5 Dec 90 18:24:42 GMT References: <4551@umbc3.UMBC.EDU> <184e255a.ARN04328@adspdk.UUCP> Reply-To: daveh@cbmvax.commodore.com (Dave Haynie) Organization: Commodore, West Chester, PA Lines: 42 In article limonce@pilot.njin.net (Tom Limoncelli) writes: >In article <184e255a.ARN04328@adspdk.UUCP> hclausen@adspdk.UUCP (Henrik Clausen) writes: >> In article <4551@umbc3.UMBC.EDU>, cs472119 writes: >> >[ If I plan on getting an '040 card for my Amiga 3000 is it better >> > to have a /16 or a /25?] >Now I've heard that question answered both ways. The person that >opposed the above answer was one of the designers of the Amiga 3000. >Basically, the Zorro III bus is effected by the speed of the system so >the faster you get your Amiga 3000, the faster the '040 will be at >certain operations. Ok, lemme settle this. First of all, we're confusing the issue here a little. The speed of a Zorro III bus transaction is determined, within some reasonable physical limits, only by the speed of the bus master and slave involved in that transaction. When the A3000 motherboard is acting as Zorro III bus master, the A3000 motherboard's system clock determines the speed of the transaction, because of the way I happened to design that bus controller. Any bus master you put into the Zorro III bus will run that bus at its speed, not at the A3000 motherboard speed. None of which immediately concerns anyone anyway, since 68040 cards don't likely sit on the Zorro III bus, but instead in the Coprocessor slot. Now, the Coprocessor slot is set up to be very flexible, and allow a card to be designed to act either synchronous to the A3000 bus clock or asynchronous to the A3000 system. Since the 68030/(68881|2) in the system are the only parts that are different between an A3000/16 and an A3000/25, we made it possible for a Coprocessor card to drive the A3000 system bus clocks on its own, leaving the on-board processor driven by its on-board clocks. So a Coprocessor card can run a 16MHz system's motherboard at 25MHz. The on-board 68030 will of course still only work at 16MHz, so it must be shut off in any such setup. With a 25MHz A3000, you might have both Coprocessor board and on-board 68030 running at the same time at 25MHz. That's the only thing you can't do on a 16MHz system than you can on a 25MHz system. >tlimonce@drew.edu Tom Limoncelli "Flash! Flash! I love you! -- Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy Wheeeeeeeeeeeeeeee...........