68882

[Dal]

Does anyone know of a supplier of MC68882's in UK?

[Greenious]

On ebay 68882:s regularly show up for around 5 euros.

Don't know of any specific UK vendor though.

[simbo]

look also for old macintosh machines like proforma
and others of the same ilk as atari {1980-95}

most macs have a coprocessor and a nice stick of ram to reuse

proforma is exaclty right it has a 16mb partiy or non parity ram
{some have non most are parity}
and nearly all ive found in the street have the co processor
and usualy a 33mhz type to fit the needs
then there is no hasle with ebay and very little if any bill

you can pick these machines up in jumble sales car boots or on the street
or under the stairs
its the kind of poo machine the old man used for word docs
and now props open the door or has a pile of books on
and a layer of dust
also has a 400 or 1gb scsi2 drive !!! and a 68060 or 68040 mpu

[Dal]

Got mine from Best Electronics this week. Works a treat!

[nativ]

So as i understand it.

you can use a 68881 @ 16mhz
or the
68882 @ 16/25 or 33Mhz
And the falcon will be happy with the different speeds of FPU. With or with out an accelorator.

I suppose 16/32 will be carrying System Solutions old stock now,
for a retailer in the UK?

Ashley

[Greenious]

And the falcon will be happy with the different speeds of FPU. With or with out an accelorator.

More or less correct. But the actual speed the FPU is being run at, is 16 MHz, since that is what the mobo feeds it. You have to do some soldering to feed another clock to the FPU if you want it to run faster.

So a standard F030 will accept any 6888x. (Don't think they ever made one slower than 16 MHz)

However, considering the 68882 is something like 50% faster than 68881, and the 68881 is better suited for some applications running on ST/STE, I would get a 68882 for the F030. And if you happen to find a 68881, I am sure that someone with ST/STE would be more than happy to swap it for a 68882, since 68881 are somewhat rare.

[atarimusic[dot]net]

I'm curious. If the system bus is limited at 16MHz, what good does it do to overclock the FPU up to 50MHz? Will things really run faster or is the difference so minor that it only exists in theory and not for practical purposes (i.e. using Cubase, watching demos).

[Frank B]

I'm curious. If the system bus is limited at 16MHz, what good does it do to overclock the FPU up to 50MHz? Will things really run faster or is the difference so minor that it only exists in theory and not for practical purposes (i.e. using Cubase, watching demos).

From a scan of the 68882 manual it appears the first part of the pipelined instruction execution time is dictated by the host cpu clock. The second part is dictated by the FPU clock. I'd guess the ideal would be clocking both of them with the same frequency. Otherwise the CPU might not be able to keep the FPU busy. This is just a guestimate from reading the docs though.

Frank

[wongck]

Demos may not be faster.... because they are normally optimised and have "stuff" precalculated in tables and values obtained via a simple lookup (lookup table).

Of course speeding up the FPU will show up and be felt if the application uses alot of it. Here are some benchmark on before and after by just overclocking the CPU done by dexterlabs recently. Some 25% increase.
So if the application is using FPU 20% of the time, you will probably get something like 5% (20% x 25%) speed increase overall.
That's the part that uses the FPU.

What this 68882 or 68881 does is enable applications that needs a FPU to run works - like zView where you can view (for example) PDF files.
This, for me, is the greatest benefit.

[EvilFranky]

Ah so Zview uses the 68882 to process the vector fonts used in PDF docs? That very cool.

How quick can a standard 68882 equipped Falcon render a PDF?

[atarimusic[dot]net]

The other gentleman here on this forum, Simbo, suggests that if you're not interested in overclocking the Falcon's FPU, the 33MHz version is still better than the 16MHz. He says that is has less "pin glitches". Any chance this chip would run better, faster, than the 16MHz? What about the 1MHz overhead it has?

Fascinating answers btw guys. I'm not a computer tech - just an Atari musician trying to understand another realm of Atari altogether.

[wongck]

Ah so Zview uses the 68882 to process the vector fonts used in PDF docs? That very cool.
How quick can a standard 68882 equipped Falcon render a PDF?

Unfortunately I do not know, on a stock Falcon with 68881/2, the time it takes.
My machines are TT with 68882 and Falc with CT63.
On the TT, it does take a fair bit of time to decompress it (but no timing information) compared to Wintel viewing PDF.
So my guess is that a Falc will take twice that time - 32MHz vs 16MHz.

[wongck]

The other gentleman here on this forum, Simbo, suggests that if you're not interested in overclocking the Falcon's FPU, the 33MHz version is still better than the 16MHz. He says that is has less "pin glitches". Any chance this chip would run better, faster, than the 16MHz? What about the 1MHz overhead it has?

I am sure that there are some internal mechanism that improves the 68882 from the 68881. As to what they are, may be you need to find out from the 68882 devices specification from Motorola.

[Shredder11]

Does anyone know where we can buy the 68882 for our Falcons? A quick search has only found one on USA Ebay and it is the 25MHz model (MC68882FN-25A) for approx 25$ / £16. Also one on eBid USA for 21$ / £14 but this is the slowest 16MHz model. I've seen a post on the net from 2007 saying they only cost about 5 EURO, so does anyone know where we can buy them at similar prices?

[dexterslab]

you'll probably have to do weekly searches on ebay until one comes up

solong as the chip is rated the same or faster than you want then it'll be fine. From what i've read the 68882 can be overclocked by a good margin, don't forget that the cattermaran runs the tt's 33mhz 68882 at 48mhz so i'm sure a 20 or 25mhz version would be fine at 32mhz

[alexh]

We had this conversation once before. There was only ever one version of the MC68882 die meaning that all chips are exactly the same. There is no difference between a 16MHz version and a 50MHz version.

There is a slim chance they were "speed-binned". Tested to see what speed they would operate at and separated. However towards the end of their manufacture the yields are likely to have been so high. They probably just marked up chips according to demand.

[wongck]

That explains why they are so overclockable.