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jessenator

IIsi chipping with FPU

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So I've found a specific, incredible resource here regarding chipping and the limitations specific to the IIsi, what I'm looking for is this:

 

I'm planning on getting the PDS riser with fpu socket and need some guidance on which specific fpu p/n to look for.

 

I know it's a 68882. I'm guessing it needs to be 20MHz like the 030 that it'll pair with, and then the crystal oscillator change (55mhz) will change the clock of both?

 

Thanks

Edited by jessenator

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Is it the mc68882fn20? I did an image search, but that's not always accurate...

 

The mc68882rc20 looks like one that would go into a pin socket.

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Did more searching and the PDS risers definitely use the MC68882FN20. Now, here comes more digital circuitry noobery: does the variant matter? on ebay I'm seeing "MC68882FN20A" FPUs with a mask of 2C12R. From the reference photos I see, included FPUs are "MC68882FN20 1C12R" 

Also, some cards have a crystal OSC on them, at 40MHz, mirroring the crystal OSC on the main board. If the expansion board I'm going to use has no oscillator, what would that mean in a chipping situation?

Edit: so I'm seeing a crystal oscillator only on the Apple NuBus adapter, but not on the Superamac, Daystar, and unbranded PDS risers.

Edited by jessenator

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So the definitive/consolidated chipping guide on the site has dead (?) links as far as detail is concerned.

 

LowEndMac stated inconclusively that the Apple branded PDS-to-NuBus riser's FPU might not function at the same speed if the main oscillator was replaced or interrupted.

 

Since they weren't expensive I ordered a new oscillator. Will probably socket the pins so I can easily replace them.

 

Has anyone tried this with a non Apple fpu riser and gotten results one way or the other?

 

On mobile I cannot relocate the thread I discovered earlier stating that the ceiling for retaining other hardware support, like floppy drive, was 27.5 MHz . Other threads are saying it's only 25?

 

Anyway, a working link to the IIsi workflow would be greatly appreciated if there's no one who's done this and can comment.

 

Thanks

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Ok, I think I've got a better scent on this trail. Sorry for the excess of self-posts, but it took a bit of digging so hopefully this helps IIsi users going forward:

The original "consolidated thread" does indeed use outdated links, but hopefully this will clear that up, at least for me, hopefully others. This is uniserver's page that I'm referring to, with the outdated-format links


Here's the OC page (I think) he refers to specifically regarding the IIsi he swapped the crystal on

At the original OC speed of 29MHz they note that aside from the FPU (question answered there) the adapters do not function correctly. But others as in this thread state that 25–27.5 work, but don't mention PDS/NuBus riser issues

But, in another outside site's page whose link is outdated, this is apparently mentioned (emphasis added):

Quote

 

I have done this to a few IIsi, and the highest frequency we could get to work

without problems was 27.5MHz. Thus a speed increase from 20 to 27.5MHz. The

actual crystal is 55MHz (double the frequency). 55MHz TTL crystal oscillators do

exist, but they are rare. The thing most people seem to do is get a 55MHz CMOS

oscillator, and they work just fine. At 58.9 and above, there are problems with

the floppy drive; you cannot boot the Mac from a floppy, but other than that it

is fine until just over 30MHz. I recently had a IIsi at 28.3MHz and it was fine.

Be warned that some NuBus cards may not work after this modification. Most will

work at 25MHz, but will not at 27.5MHz, so just stick with 25MHz if that is the

case.

 

This was the link: http://bambam.cchem.berkeley.edu/~schrier/mhz.html but not even on wayback machine could I find it.


Well I think that about covers it. It'll be a nice experiment, to be sure!

Edit: also, I apologize as this should have been in the Hacks & Development forum :( 

Edited by jessenator

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