Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ukma!xanth!lll-winken!uunet!cbmvax!daveh From: daveh@cbmvax.UUCP (Dave Haynie) Newsgroups: comp.sys.cbm Subject: Re: what is this chip(65C802) Message-ID: <6491@cbmvax.UUCP> Date: 4 Apr 89 18:28:10 GMT References: <16510@cup.portal.com> Organization: Commodore Technology, West Chester, PA Lines: 99 in article <16510@cup.portal.com>, A-N-Onymouse@cup.portal.com (John - DeBert) says: > In article <6460@cbmvax.UUCP> daveh@cbmvax.UUCP writes: >>Sounds like you've been reading GTE databooks. One caution -- don't believe >>everything you read. While these databooks often show the timing for parts >>in a wide variety of speeds, that doesn't necessarily mean that such parts >>are actually available. Last time I looked, GTE listed 65C02s up to 4MHz and >>65C802s and 65C816s up to 8MHz, though they only had 4MHz versions of the >>latter, and no real yield on the former at 4MHz (they probably have the >>4MHz 65C02s by now...). > Hmm. I have before me a copy of a data sheet for the WD65C816/65C802 that > specifies a version of the device with an 8MHz clock. It's >NOT< a preliminary > data sheet. The Western Design data sheets are just as misleading. You really have to consider what a data sheet is. You seem to think that it's a description of what a particular part does. In reality, all a data sheet for any part tells you is that, given a particular part, what's the worst that you can expect from it. It's a specification, just as it says. If Western Design or GTE were to make an 8MHz 65C816, it would have to meet that specification. Just because they've produced a specification is absolutely no indication that such a part exists or ever will exist. I had the specification sheets on 65C816s, going all the way up to 8MHz, back when the fastest part they could make was a 500kHz version. > 8MHz is too fast for DRAM? Shhh! Don't tell my HP! It has DRAM and an 8MHz > clock. Plus a faster one for the alphagraphics display. :) > Seriously, one wonders how one may get DRAM to work with those so-called > turbo clones with clocks of at least 8MHz. If you don't understand the difference, I hope you're not going to be designing any PC clones or 6502 systems in the near future. The clock speed given had absolutely no standard relation to bus speed (bus speed directly relates to the possible memory speeds you can deal with). The 8086 family runs one memory cycle in 4 CPU clocks, the 6502 family runs one memory cycle in 1 CPU clock. So your 8MHz 8086 machine is, from the point of view of the memory you have to support, roughly equivalent to a 2MHz 6502 family machine, like the C128. Obviously, the C128 works just fine with moderate speed DRAM, as do most PClones. > Also, I have seen 70ns DRAMS advertised from time to time. Yes, you can get 70ns DRAMs, though they're around 5x-10x the price of 120ns DRAMs. A 70ns DRAM gives you something on the order of a 110-120ns cycle time, which is still too slow for an 8MHz 6502 family processor. Part of the problem here is the 6502 design itself. The memory cycle time of a 6502 family part at 8MHz is 125ns. The problem is that, unlike modern CPUs such as the 680x0 family processors, the 6502 doesn't give you much help in closely matching a memory system to the CPU. The 680x0 parts give you a strobe when addresses are valid and a strobe when data is valid, and both address and data come out really fast. The 6502 just gives you a fixed time from the falling edge of PHI0 to when addresses or data are valid, things like that. So you can't design a circuit that's nearly as tight as a 680x0 circuit, even if address/data events were as fast for the same bus cycle time (which they aren't). > I doubt that it would be worth the trouble and expense to modify the C64 > for "turbo speed" using the 65C802. There would need to be drastic changes > in bus timing and how interrupts were handled. Well, for turbo speed, you really can't modify the C64 bus timing, you just build a separate 6502 computer with fast memory that knows when to slow down and access the C64 resources. The 65816 accelerator thing I mentioned. I still doen't recall the manufacturer, though I saw it last at the Philly World of Commodore, running BASIC at 4MHz, though I believe they've modified the ROMs to drop down in speed when accessing disk and any other time critical things. And most video games will die or at least malfunction with a faster system. Nothing changes with interrupts themselves, though any routines driven by interrupt code, like raster interrupts for screen splits or reusable sprites almost always depend on processor wait loops, which of course are directly based on the speed of the 6502. Fred's certainly seen most of what can go wrong from back in the C128 days. >After you're done with the mods, you'll probably never be able to put the > thing back in a C64 case. Even if you just wanted to do a straight > replacement of the 6510, there's still the problem of how to implement > the i/o port but that's not really too hard. The commercially available units typically plug into the expansion port, and to do much of anything, new code is required. All in all, though, I agree; it would be more trouble than it's worth to try and build such an accelerator, unless that just sounds like a fun hobby. If you want a faster C64, I'd recommend buying one of the commercially available units. > Ah, well. Now that we've knocked your idea and all, perhaps you'll prove us > all wrong? :) Maybe he will. After all, someone had to design the ones that are already out there. >>Dave Haynie "The 32 Bit Guy" Commodore-Amiga "The Crew That Never Rests" > J. DeBert -- Dave Haynie "The 32 Bit Guy" Commodore-Amiga "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: D-DAVE H BIX: hazy Amiga -- It's not just a job, it's an obsession