Overclock SupraTurbo28?

[Cyberus]

I was just wondering if anyone had any thoughts on this?
It'd just be 'for the hell of it'.

It contains a 68HC000@28Mhz. By looking at pics at amiga.resource.cx, I see no crystal, hmm...can someone enlighten me please?

[Piru]

@Cyberus

A500 uses 28MHz clock internally (/4 is used for CPU), and AFAIK this clock is provided thru the expansion slot, and is used by Supraturbo 28.

That is, you can't overclock the board, without also overclocking the motherboard. That'd also skew system timers and such, and make display, floppy etc misbehave.

[Cyberus]

@ Piru

Hi, I thought the 86-pin expansion slot was was missing the 28MHz signal -  (pin 9 on the A2000 CPU fast slot)

edit:
If it isn't missing the signal, wouldn't it be possible to easily use  an A2000 CPU card with the A500, since the 28Mhz signal would be present...

[peroxidechicken]

I used to have one of those - it worked on my a500 and also on my a2000.  I think there was a sticker or something on the cpu - when I took it off I found that my particular cpu was actually a 16MHz one but it never had a problem running at 28MHz.  

[Schoenfeld]

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

[zipper]

I've seen some comments about running ST28 at 40 MHz - all hard facts are missing yet...

[Cyberus]

Thanks for your replies Jens

Schoenfeld wrote:
The 28 Mhz signal is not available on any of the expansion ports of any Amiga.

So not even on the A2000 CPU Fast slot?
There's a pinout at the Big Book of Amiga Hardware that says   pin 9 is 28Mhz...what does this mean?
[/quote]http://amiga-hardware.com/a2000cpu.html

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.

So how does something like the DMA expander work (allows the use of A2000 accelerators in A500)?
http://amiga.resource.cx/exp/search.pl?product=dma+expander&company=
I was assuming that it generated the 28MHz signal (as shown in the pinout of the A2000 CPU fast slot)

The A500plus provides the 7Mhz signal on the 86-pin port, but no design ever used this, AFAIK.

So the pinouts are very slightly different between the A500 and A500plus?

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.

Shame

[Deadbeat]

Not quite true. I have the SupraTurbo28 in my A500+ and I simply replaced the 28.xxx MHz crystal in mine with a 36 MHz one already in 1996 or so.
Has worked like charm ever since. No additional cooling (like huge heatsinks or fans) or decoupling tricks required either!
Friend's ST28 went up to 40 MHz, that's because his cache SRAM chips were faster, mine couldn't keep up with that, hence "only" 36 MHz for me.