Crystal osc for Blizzard A1200/4 + 68882 FPU

[Hodgkinson]

Hi there,
What crystal should I get from amigakit for my Blizzard A1200/4 RAM board in order to compliment a 68882 33Mhz FPU unit?

I see that the BBOAH shows the board with a 30.000Mhz oscillator installed, yet the closest amigakit supply are 28.6363Mhz and 33.330Mhz oscillators.

Comments appreciated,
Hodgkinson.

EDIT: Ooops, just checked. BBOAH shows a 32.000Mhz osc.

[meega]

The 33MHz.

Edit: My opinion. It's right for the fpu, and gives 5 million more clocks per second for the fpu to do its stuff. (There is no requirement for a 68882 to run at cpu speed, or even an integer multiple of that speed. The more clock cycles available to it, the better.)

[Hodgkinson]

Hmmm.
I've just been looking at the MC68882 datasheet from www.alldatasheet.com and under page 38 for the AC Electrical specifications - Clock input there is a max of 33.33Mhz under the 33.33Mhz coloum.

The 33.33Mhz osc might just be spot on for the FPU by the looks of this.

Just thought i'd post the info,
Comments still appreciated,
Hodgkinson.

[meega]

Is *your* fpu a PLCC (Plastic Leaded Chip Carrier, i.e. resin square with metal prongs round the sides, sits in a socket) or a PGA (Pin Grid Array, i.e. ceramic square with pins all over the bottom, sits into a grid of holes) type of fpu?

[rkauer]

 We have discussed this before.

 The conclusion is: better not run 68882 in clocks ABOVE the CPU clock. No problem if the crystal is 33.33 MHz or integer 33 MHz (1% IS nothing).

 But better put some heatsink &/or a little fan over the coprocessor (it runs very hot, specially the 50 MHz version).

[meega]

@rtkauer, I don't quite understand what you are saying.

@Hodgkinson, I see from this that the card does not have a CPU, only an FPU (PLCC) and some RAM, and should already have a crystal. What are you trying to do?

[rkauer]

meega wrote:
@rkauer, I don't quite understand what you are saying.

@Hodgkinson, I see from this that the card does not have a CPU, only an FPU (PLCC) and some RAM, and should already have a crystal. What are you trying to do?

Hello meega, no, I not discuss WITH you, I mean we discuss HERE in A.org putting a coprocessor FASTER than the CPU itself makes the acelerator unstable.

Nothing to worry about RAM expansions with coprocessors, tought.

[meega]

rkauer wrote:
Nothing to worry about RAM expansions with coprocessors, tought.

I thought we were discussing an expansion card.

(Sorry about the typo in your name, well corrected in your quote.)

[Hodgkinson]

Thanks for the replies.
The A1200/4 board that I have doesn't have the FPU or the crystal installed. Presumably the FPU/Crystal is a optional extra. The FPU accepted is the PLCC (Black plastic case, small metal pads around the edge) type 33Mhz clock.

When I get the FPU i'll check the temp after a while of running.

Btw, the A1200/4 isn't a coprocessor board. Its just a RAM board with a RTC and (Presumably optional) FPU.

Regards,
Hodgkinson.

[meega]

It's designed to work with **no** additional cooling. It does not need a fan, or heatsink, or anything else. Just fit it (and the crystal) into the card, fit the card into the machine, and forget it.

I have a different A1200 expansion with such an fpu, at 33MHz, and it worked fine at rated speed. I don't think the PLCC fpu's will overclock very well, though, as I had crashes after an hour or so at 40MHz - which ceased on refitting the original crystal.

[rkauer]

I use an overclocked CPU and FPU here. Put a 52 MHz crystal (the original was 50). Heatsinks in both chips, a lateral notebook fan and all runs smoothly.

No need to say there is a minor overclock (4% is almost NOTHING). But gives me a bit more speed, anyway.

BTW: I have a Microbotics 1230XL (PGA chips, who have that metal cover, so put an extra heatsink is a good thing) with 128Mb RAM in here.

[meega]

@rkauer, Your expansion card is full! Do you happen to have any 50MHz PGA 68882's available?

[rkauer]

Sold a year ago... :-(

[Hodgkinson]

Thanks for all the advice!

I've now ordered a 68882 and 33.33Mhz Crystal from AmigaKit. Should arrive any time soon.

Regards,
Hodgkinson.

[meega]

Hope it works well for you. (I'm sure that it will.) Make sure that you put them in the right way round (dots at the right end/side).