Classic II FPU card design

[maceffects]

Maybe someone can correct me but I thought the the speed should match the speed of the processor?  Shouldn’t they be 16mhz/16mhz?

 

[LarBob]

Maybe someone can correct me but I thought the the speed should match the speed of the processor?  Shouldn’t they be 16mhz/16mhz?

Nope, see the datasheet for the MC68882 (specifically page 5-98/PDF page 3). The CPU and the MC68882 work fine together at different clock speeds.

 

[maceffects]

Nope, see the datasheet for the MC68882 (specifically page 5-98/PDF page 3). The CPU and the MC68882 work fine together at different clock speeds.

Thanks, I remember some processors used to be really fussy about that. I’m glad this allows for flexibility. 

 

[moldy]

Thanks, I remember some processors used to be really fussy about that. I’m glad this allows for flexibility. 

If you look at my screenshot from MacBench, you can see the results for two frequencies (@16M and @40M; the CPU was always at the default 16M). 40M gives a slight boost to the benchmark score. The card itself has a jumper to configure which clock to use (OSC means the oscillator on the card, SYS is using the C16M signal from the logic board which is 16M).

 

[LaPorta]

Thanks everyone. So I'd definitely buy one, and hopefully Kai can give us a link to the NOS 40s...I'd be all in!

 

[mattsoft]

I don't have a Classic II, but projects like this are just awesome. Nice work moldy!

 

[Kai Robinson]

Thanks everyone. So I'd definitely buy one, and hopefully Kai can give us a link to the NOS 40s...I'd be all in!

Well, you can buy individually, or i can order a load en-masse, and distribute?

https://www.utsource.net/itm/p/1862306.html

 

[LaPorta]

Man, is that shipping ever steep! Guess it would work out if as you said we distributed, but not from the UK I sould suppose.

 

[Paralel]

I am currently working on a derivative of this design that would support the 50 MHz part 68882. It's a PGA, which is the only major difference between it and the rest of the 68882 series. The only reason is "because". Sort of like most of the projects for 68k Macs.

 

[moldy]

I am currently working on a derivative of this design that would support the 50 MHz part 68882.

Super cool, glad to see someone picked up on this, let us know how it goes!

 

[tashtari]

Any good place to get one of these assembled? A Classic II recently came into my possession and I'm interested in giving it toys, but my soldering skills are pitiable.

 

[moldy]

Any good place to get one of these assembled? A Classic II recently came into my possession and I'm interested in giving it toys, but my soldering skills are pitiable.

I realized I still have two units of my original batch that I planned to sell (but the thread disappeared in the forum crash) - if you're interested just shoot me a PM!

https://68kmla.org/bb/index.php?threads/fs-2x-macintosh-classic-ii-fpu-card.40593/

 

[aplmak]

Where can you find a mc68882fn40a that’s not fake these days?? Aren’t most of them fake Chinese made ones??

 

[moldy]

Where can you find a mc68882fn40a that’s not fake these days?? Aren’t most of them fake Chinese made ones??

I sourced some genuine one from local auction sites with NOS chips. Alternatively the ones from China (Ali/eBay) even though potentially remarked, work pretty reliably and cool for me