waggoner@dtg.nsc.com (Mark Waggoner) (04/04/90)
In article <1990Mar31.223641.13301@aucs.uucp> 880274d@aucs.UUCP (Ralph Doncaster) writes: >I'll be buying a 68030 based accelerator for my Amiga, without the >68030. What I am wondering is how much can I overdrive a 68030 >beyond it's spec. I'm getting a heatsink and small fan to keep it >cool, so I imagine 20% above spec should be no problem, but I'd like >to know how much more can I go than that. (Could I run a 16Mhz '030 >at 25Mhz an not fry it?) First off, I assume your accelerator is an asynchronous design or you can't run it faster at all. I don't believe that frying the chip is what you need to worry about. Generally, the reason a chip is spec'd at a certain frequency is because the timing parameters and logical operation of the chip can only be guaranteed at that frequency. If it is guaranteed over a commercial temperature range (often 0-70 degrees C) then, assuming that the part operates slower at high temperatures (CMOS does this), you have some margin if the device is kept at room temperature (about 25 degrees C). How much margin you have is something you can only find out by trying it, or perhaps by working for Motorola. You also need to know how critical the timing specifications of the chip are to the particular design you are using. It may be that the part will logically function at higher speeds but that the timing gets out of specified limits. If the design can tolerate this, then you can go faster. Of course it is also possible that the board was designed for room temperature operation and never tested under hot conditions and so you have little or no margin at all. When you run parts out of spec, experimentation and a willingness to risk unreliable operation are required. -- Mark Waggoner Santa Clara, CA (408) 721-6306 waggoner@dtg.nsc.com Unofficially representing National Semiconductor Local Area Networks Group Officially misrepresenting myself.
daveh@cbmvax.commodore.com (Dave Haynie) (04/10/90)
In article <101213@convex.convex.com> swarren@convex.com (Steve Warren) writes: >In article <10598@netcom.UUCP> mcmahan@netcom.UUCP (Dave Mc Mahan) writes: >>In a short summary: >> If the chip was able to be driven faster safely, don't you think Motorola >> would have sold it as able to go that fast? >Well, I don't know how Motorola does it but a lot of companies don't have >a seperate process for higher speed devices. All the devices come off the >same die, and they test for proper function at higher speeds until they >fill their quota for that speed range. Every device on the die may be >capable of running at the higher speed. But only the first N-devices >that pass the test will be marked as higher-speed. Last I heard, Motorola has two 68030 versions, the lower speed process can yield only 16MHz, 20MHz, 25MHz, and 33MHz parts, the faster process can yield only 40MHz and 50MHz parts. The dropouts from the 50MHz process can't serve as real 33MHz parts, because their dynamic characteristics won't operate at the minimum speed required for 33MHz operation. RAM systems like cache aren't the only dynamic elements in fast CPUs; they use some really weird ideas like dynamic latching. No refresh is ever involved, because such signals are guaranteed to be relatched if the CPU is run at the appropriate speed. These designs not only make the part smaller, but faster. Not something people thinking about standard TTL based system level design like to think about, but when you consider than some signals get in and out of the CMOS 50MHz 68030 much faster than the best F series TTL parts, you have to figure that something's up. You really never know how a process yields, and that's why overdriving any part is a really bad idea. You're OK when things work 100%, and you're OK when things fail (eg, you fix them, slow down the clock, and they work again). But when they start acting flakey, you may waste a great deal of time on a couple of bits dropping here and there. You have to depend on a reliable computer system. You can't know if the 25MHz chip you put in last January at 33MHz is going to be 100% this summer in your 90F computer room, no matter how nicely it acted this up to now. >--Steve DISCLAIMER: All opinions are my own (I don't speak for Convex) -- Dave Haynie Commodore-Amiga (Systems Engineering) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy Too much of everything is just enough
LDSHANER@MTUS5.BITNET (Leon D. Shaner) (04/12/90)
A careful re-reading of the original post should reveal that what this person wants to do is buy an accelorator card designed for say a 25Mhz CPU and through a 16 Mhz CPU in it.. Quite a different story than taking a board designed for a 16MHz CPU and trying to mod it to run at 25 MHz Of course I may have misunderstood, also... +--------------------------------+-----------------------------------+ | LEON D. SHANER <LDSHANER@MTUS5> :BBS: AMIGA BITSWAP CENTRAL DISPATCH: | EE UNDER GRAD. : (906)487-0006 <-AMIGA ONLY! : | MICHIGAN TECHNOLOGICAL UNIVERSITY : FREE! - 24 HOURS - 80 MB : +------------------------------------+-----------------------------------+