FPU VS jumpers

[Lord Aga]

Sooo. I can't seem to guess the jumper combination needed for 68881 FPU to be enabled.
The card in question is BC 1208ma. Here's the picture, and any suggestions would be welcome

[Franchute13]

maybe like .....
http://www.bigbookofamigahardware.co...s/bc1208ma.jpg
see J9 and J8 jumper

[Lord Aga]

It wont wake up with this configuration

[prowler]

J7 - Enable FPU, as shown in your picture.

Change from open to closed.

[roy bates]

have you got a oscilator on board?

[Lord Aga]

@Prowler
Whenever I close J7 it wont wake up at all.

@roy
No oscillator, as seen on pic.

[roy bates]

have you tried multiple jumpers?

like j7 closed,j8 and 9 set to pga?

[Lord Aga]

J8 and J9 are quite unclear. Numbers imply vertical jumper orientation, but "PGA" and "PLCC" writings on the left imply horizontal jumper orientation. No idea what's right

[roy bates]

Originally Posted by Lord Aga

J8 and J9 are quite unclear. Numbers imply vertical jumper orientation, but "PGA" and "PLCC" writings on the left imply horizontal jumper orientation. No idea what's right

yes i can see that,but i have an idea.

have you got a multimeter? you could buzz out the bottom left pin of the oscilator socket and see if it joins to the bottom two pins on j8 and j9.

and take a picture of the underside of the card in that area.

[prowler]

J8 and J9 are confusing.

It appears that there are three jumper positions: top, centre and bottom pairs jumpered. These would correspond to PGA FPU (Roy's suggestion), PLCC FPU and External (FPU or oscillator?). But why is this jumper set labelled J8/J9. Surely just J8 or J9 would do if that's how they work.

[Lord Aga]

@roy
You mean to check if these are connected ?

[roy bates]

Originally Posted by prowler

J8 and J9 are confusing.

It appears that there are three jumper positions: top, centre and bottom pairs jumpered. These would correspond to PGA FPU (Roy's suggestion), PLCC FPU and External (FPU or oscillator?). But why is this jumper set labelled J8/J9. Surely just J8 or J9 would do if that's how they work.

im thinking that there like that to select the socket AND external clock,can you see it prowler?

[roy bates]

Originally Posted by Lord Aga

@roy
You mean to check if these are connected ?

no,i have a feeling its the bottom two,but check them as well.its just for confirmation.

its to find out where the oscilators output goes on the jumpers.

basicly buzz them out in pairs and see which ones are connected and direct the clock signal to the socket in use.

it must have an internal clock and external,external being the oscilator socket output.

so its like a process of elimination.

[prowler]

Originally Posted by roy bates

im thinking that there like that to select the socket AND external clock,can you see it prowler?

Yes, but what does 'external clock' mean in this context?

Is it possible to share the motherboard's clock signal with the CPU, or is it necessary to provide yet another clock input if the expansion card's X-tal socket isn't populated?

[Lord Aga]

@roy
Just checked. These two are connected.



@prowler
As I understood with some other cards, without external oscillator FPU will work at CPU's frequency (14MHz here). But with external oscillator FPU's frequency can be higher (which is not that important to me really).

[prowler]

Originally Posted by Lord Aga

@roy
Just checked. These two are connected.

@prowler
As I understood with some other cards, without external oscillator FPU will work at CPU's frequency (14MHz here). But with external oscillator FPU's frequency can be higher (which is not that important to me really).

Then I think you should close J7 and the top (PGA) pair of J8/J9.

[roy bates]

yes and yes to both lads,thats what im thinking.


now,check to see if the pin thats connected to the oscilator output is also connected to the pin directly to the left or directly above the one you marked in the picture.

if it isent connected to either..

[Lord Aga]

Originally Posted by prowler

close J7 and the top (PGA) pair of J8/J9.

Wont wake up with this combination

Originally Posted by roy bates

now,check to see if the pin thats connected to the oscilator output is also connected to the pin directly to the left or directly above the one you marked in the picture.

if it isent connected to either..

It is not connected to either

[roy bates]

im tempted to guess a horizontal jumper across where its says pga.(close the top two pins)
logicly that would make sence no?
have you got a picture of the other side of the card?

[prowler]

Originally Posted by roy bates

im tempted to guess a horizontal jumper across where its says pga.(close the top two pins)
logicly that would make sence no?

That's what I was suggesting in my last post, but Lord Aga said that didn't work.

I'm wondering whether the true purpose of linking J8 and J9, as shown in Franchute13's link, is meant to provide a clock signal to both the PGA and PLCC sockets for use with either type of FPU. But Lord Aga said that didn't work either.