The 28 Mhz signal is not available on any of the expansion ports of any Amiga. The Supra accelerator probably generates it with a PLL.
What's missing on the A500 86-pin connector is the 7Mhz CPU clock signal, but that can be generated by X-ORing the two 3.5Mhz signals, so I guess Supra just took one of these 3.5Mhz signals and multiplied them by 8.
The A500plus provides the 7Mhz signal on the 86-pin port, but no design ever used this, AFAIK.
The 16Mhz 68000 CPU of the Supra Turbo28 was a CMOS version, it hardly gets warm when overclocked, but since the rest of the thing is fully syncronous, overclocking will NOT work. Only async designs can be clocked at "any" frequency.
Jens Schoenfeld
