Amiga 1200 motherboard FPU upgrade?

[SpeedGeek]

Originally Posted by eXeler0

@gdunlapsd If there was an elegant way to do a mod when a 40 or 50MHz Crystal then I'm sure it would be a popular mod ;-)
Just got me thinking what happens if you have an onboard FPU and a TF1260 with an EC060 ;-)

The EC060 does not have the co-processor interface logic required to communicate with the FPU. But even if it did the EC060 would trash the performance of any decent 68060 accelerator card anyway.

[gdunlapsd]

Actually, it turns out that you can use a faster crystal, for whatever speed your FPU can handle

I hooked up the clock wire to a 50mhz crystal oscillator, and using a known good 40mHz 68882, it works fine! Hardly gets lukewarm.

I did get a weird crash once, so I decided to copy the circuit the A1200 has for its 28mHz crystal by having the crystal's output connected to 5v via a 470 ohm resistor, and to the FPU via a 68 ohm resistor. Seems to be completely stable now.

I'm using one of those 4-pin crystals that fits a DIP socket; like this:

https://www.digikey.com/en/products/...0AX-500/827244

It benchmarks a little slower than others report with FPUs integrated into the accelerator, probably due to some bottleneck in communicating over the 14mHz bus, but it's still pretty good.

Originally Posted by eXeler0

@gdunlapsd If there was an elegant way to do a mod when a 40 or 50MHz Crystal then I'm sure it would be a popular mod ;-)
Just got me thinking what happens if you have an onboard FPU and a TF1260 with an EC060 ;-)

[ifrit05]

Originally Posted by gdunlapsd

... I hooked up the clock wire to a 50mhz crystal oscillator, and using a known good 40mHz 68882, it works fine! Hardly gets lukewarm...

Would love to see the process for this and/or pics!

[gdunlapsd]

Originally Posted by ifrit05

Would love to see the process for this and/or pics!

Here you go:

Via to FPU clock pin bypassed as described earlier:



50Mhz crystal oscillator; +5v and ground wired to each side of the capacitor to the right of the little perfboard.
The perfboard is secured with a piece of double-sided foam mounting tape.
The Output is connected as I described above:

x out --------/\/\--------> FPU Clock
           |   68 Ohm
          /
          \ 470 Ohm
          /
          |
      +5v

AIBB "Flops" benchmark results: