Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!cbmvax!daveh From: daveh@cbmvax.commodore.com (Dave Haynie) Newsgroups: comp.sys.m68k Subject: Re: 68040 for 68030 substitution (question) Message-ID: <22239@cbmvax.commodore.com> Date: 7 Jun 91 07:48:37 GMT References: Reply-To: daveh@cbmvax.commodore.com (Dave Haynie) Distribution: comp Organization: Commodore, West Chester, PA Lines: 31 In article alanr@media-lab.media-lab.media.mit.edu (Alan Ruttenberg) writes: >I was wondering if a 68040 can be substituted for a 68030 in a >MacIIfx. I understand that the pinouts and the clock rate (40Mhz 030 >25Mhz 040) are different. Considerably different. The 68040 bus is completely different than the 68030 bus. There's no dynamic bus sizing. All normal memory cycles are "burst" cycles, even writes in the preferred operating mode. The '040 runs from two clocks: BCLK, which determines the bus speed (25MHz is normal) and PCLK, which determines the ALU speed (50MHz on a 25MHz chip). There's no real practical way to kludge this into a 68030 socket, though I suppose someone will do it anyway. Perhaps if the IIfx has some kind of slot designed for a 68040 card, you could build an upgrade. This is what we did on the Amiga 3000. >What I am curious about is what a minimal upgrade to a 040 would >entail. Can I buy a chip, and build a small adapter board? Or are >there many changes that would have to be made. First of all, you need a bus conversion state machine, which will translate 68040 signals into 68030 signals. This isn't all that difficult, if you're real familiar with 68030 signals, but it's not something you'll hack together in a weekend. You also need bus bridging buffers to handle whatever subset of the 68030 bus sizing mechanism the IIfx requires. In other words, you need the Motorola hardware documentation. They do have an appnote on an example 68040->68030 bus converter, which might be a good starting point, even though it looks a little bloated. -- Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy "This is my mistake. Let me make it good." -R.E.M.