Macintosh Classic II FPU card
Macintosh Classic II FPU card
This project is about an expansion card that adds an MC68882 FPU to your Macintosh Classic II. The board has two layers to keep the PCB cost down. It offers a switchable clock source between the system clock (16 MHz, synchronous operation) and a crystal oscillator on the board (40 MHz, asynchronous operation; tested with MC68882FN40A, the rumours claim 50 MHz will work too).
Results
After plugging in the card, it should be immediately visible in some tools (here System Information of MacBench):
The board dramatically improves the Floating Point performance of the computer. MacBench 1.0 with an FPU@16 MHz (system clock) reports over a 13x improvement. When using an external 40 MHz oscillator, the Floating Point result goes up even a bit more - to 15.7x (it's not proportional to the clock frequency as at some point the slow 16-bit bus becomes a limiting factor):
(look at the Floating Point row)
References
The MC68000 KiCAD library from https://dev.sigpipe.me/DashieElectronics/Jackalope
Macintosh Classic II FPU card
*PCBWay community is a shared platform and we are not responsible for any design issues.
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- AlDunsmuir Sep 12,2021
- Olivier Caron Jan 28,2021
- Drake9800 Jan 28,2021
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