No bios options?

Could you add a full pic of the board? Helps finding the model.

Ernesto22 wrote on 2024-11-25, 02:53:

Hi,
I bought this 286XL from ebay and can´t get it to work, boots up OK but can´t run anythig to test the NPU, it freezes instantly.
changed the CKM jumper but then it doesn´t boot up...

we do not even know what board you are running, the picture does not help much. Need more info

The Intel c80287XL is spec to 12.5Mhz max, if you run it on a board running cpu at 16mhz or 20mhz you may need to change to Async mode (usually a jumper) and use a separate clock/crystal for it.
added: Generally the 287 runs 1/3 cpu clock if driven by same cpu clock so in that case you might be ok but will be running at 13.3mhz, depending on things it may work or not.
Added2: the c80287XL is divide by 2 on CKM pin (not same as std Intel 80287) so no probably not work if run off same cpu clock, it would run at either 40mhz or 20mhz.....edit..edit..edit.. 🤣

Hi, as a rule of thumb I remember that the 80287 runs externally at 2/3 clock speed of the 80286. That's just the original type, however.

https://www.cpu-world.com/CPUs/80287/index.html

The 80287XL has an 80387 core, like most clones and runs externally at 3/2 clock speed of the 80286. It thus runs at same clock, essentially.

So an 80287XL or third-party FPU should have same MHz rating as the 80286.
Merely the old 80287 can have a slower rating.

(By using async mode, other pairings are possible, too, of course.)

For example:

If the 80286 is a 16 MHz model (running at 16 MHz), the 80287 can be a 12 MHz model (next matching model).
A 10 MHz model 80287 may or may not work.
FPUs are sensitive to overclock, though a few hundred KHz may still be okay and within tolerance.
16÷3 = 5,3
5,3×2 = 10,6 MHz

Here for 12 MHz 80286, an 8 MHz 80287 it is..
Or an 10 MHz type, if you wish.
12÷3 = 4
4×2 = 8 MHz

Never had any problems running FPUs at any motherboard speed. Last tested 286@30Mhz with both Cyrix 287XL+ and Intel 287XL.

I would guess the FPU is dead.

Nexxen wrote on 2024-11-25, 03:02:

No bios options?

Could you add a full pic of the board? Helps finding the model.

Itbreds TD60M, onlyboart missingvin the picture is that ibscured bybthe disk bay. I may have to disassemble it .. may be I will..
Thanks

Horun wrote on 2024-11-25, 03:31:

we do not even know what board you are running, the picture does not help much. Need more info […]
Show full quote

Ernesto22 wrote on 2024-11-25, 02:53:

Hi,
I bought this 286XL from ebay and can´t get it to work, boots up OK but can´t run anythig to test the NPU, it freezes instantly.
changed the CKM jumper but then it doesn´t boot up...

we do not even know what board you are running, the picture does not help much. Need more info

The Intel c80287XL is spec to 12.5Mhz max, if you run it on a board running cpu at 16mhz or 20mhz you may need to change to Async mode (usually a jumper) and use a separate clock/crystal for it.
added: Generally the 287 runs 1/3 cpu clock if driven by same cpu clock so in that case you might be ok but will be running at 13.3mhz, depending on things it may work or not.
Added2: the c80287XL is divide by 2 on CKM pin (not same as std Intel 80287) so no probably not work if run off same cpu clock, it would run at either 40mhz or 20mhz.....edit..edit..edit.. 🤣

Intresting thing that aboutvthe async mode using a different crystal. Were can I learn more about that?

Yes I saw that with CKM it woud half thebinternal clock.. wouldn't that be 10Mhz and with in range for the XL?
I tried turbo off too and didn't work.. I don't know what clock frequency would it be that way?

Ernesto22 wrote on 2024-11-25, 18:41:

Nexxen wrote on 2024-11-25, 03:02:

No bios options?

Could you add a full pic of the board? Helps finding the model.

Itbreds TD60M, onlyboart missingvin the picture is that ibscured bybthe disk bay. I may have to disassemble it .. may be I will..
Thanks

Bad wording on my side, we need the chipset model to understand what it is. In the pic it is blocked by the HDD.
This board seems not present on theretroweb.com list of mobos. Might be nice to take a good pic of the whole board, make images of the bios chips and post here a pic of the screen when it is counting ram.

Hope the npu isn't toast, rare stuff.

Ernesto22 wrote on 2024-11-25, 18:48:

Intresting thing that aboutvthe async mode using a different crystal. Were can I learn more about that?

In the 80s, there had been interposer boards with an on-board TTL quarz generator.
On the upperside, there was a socket for 80287 and a jumper.
On the lower side were contacts that plugged into 80287 FPU socket on motherboard.

Edit: To get a clean TTL signal, it might be recommended to "clean up" the signal, so that a pure square-wave signal comes out.
Something like a shift-register, buffer IC or similar had been used for that.

But aside from this, all it needs for async mode is an interposer card with a clock generator.

So an IC, clock generator, a capacitor and a jumper is all there is at most.
The principle is very simple. The 80287 just needs its own clock signal to work asynchronously from 80286 clock (resp. motherboard clock ).

Buy another 287.

kixs wrote on 2024-11-25, 21:34:

Buy another 287.

🥺😢

Like Jo22 mentioned, not all 287 math-co's can be overclocked, most have very little OC room. I have 3 and only two work in a 286-16, those are original 287-10 and -12 with the 1/3 divider (32mhz clock / 3 = 10.6Mhz. My 287XL will not because it tries to run at 1/2 or 16mhz (per Intel 80287LT datasheet with max 12.5mhz) of the 32Mhz clock. The 287LT may be fine but was designed to run with Intels 286 which peaked at 12Mhz. There are IIT 2c87 up to 20 Mhz designed to work with with Harris 16Mhz and 20Mhz cpu's.
kixs: what exact board did you: "Last tested 286@30Mhz with both Cyrix 287XL+ and Intel 287XL." That would be a 60Mhz cpu clock for 30Mhz cpu and FPU ????

This is the board's full view picture..
Hope this helps to identify and find some info.
It has a place for a fpu dedicated crystal...
And the RAM counting picture..

Ahh I so it can use a second crystal nice ! Also there is a jumper to enable ? the crystal to fpu (usually a 3 pin but yours is 2 pin).
It may be that since no crystal, it will not work with it jumped... just a guess.
Try: jumper A (jp3?) at CKM and jumper B pulled.

Kixs: some at vcfed have gotten their 287XL to work at 16Mhz but not all.... just saying you may have a very lucky one....

Here are my two 286 Max threads:
Kixs's 286 to the Max
Kixs's 286 to the Max Too

I have done a lot of testing with 286 and FPUs over the years and never had any problem. Well that's my experience 😉

I very much doubt the problem is with the speed as the FPU should work fine when the Turbo is off.

Ernesto22 wrote on 2024-11-26, 03:54:

This is the board's full view picture.. Hope this helps to identify and find some info. It has a place for a fpu dedicated cry […]
Show full quote

This is the board's full view picture..
Hope this helps to identify and find some info.
It has a place for a fpu dedicated crystal...
And the RAM counting picture..

The attachment Screenshot_20241126_004409_Gallery.jpg is no longer available

The attachment 20241126_003137.jpg is no longer available

https://theretroweb.com/motherboards/s/pcchips-m209#driver

You probably have a different version. Not in records.

kixs wrote on 2024-11-26, 08:40:

Here are my two 286 Max threads: Kixs's 286 to the Max Kixs's 286 to the Max Too […]
Show full quote

Here are my two 286 Max threads:
Kixs's 286 to the Max
Kixs's 286 to the Max Too

I have done a lot of testing with 286 and FPUs over the years and never had any problem. Well that's my experience 😉

I very much doubt the problem is with the speed as the FPU should work fine when the Turbo is off.

so are you very sure that the XL should run on my board at 20Mhz? using CKM on it is supposed to run at half the frequency... it is half the frequency of the 20Mhz bus? then it would be at 10Mhz and should have no problems, and even less with the turbo off... or am I wrong?

Horun wrote on 2024-11-26, 04:17:

Ahh I so it can use a second crystal nice ! Also there is a jumper to enable ? the crystal to fpu (usually a 3 pin but yours is […]
Show full quote

Ahh I so it can use a second crystal nice ! Also there is a jumper to enable ? the crystal to fpu (usually a 3 pin but yours is 2 pin).
It may be that since no crystal, it will not work with it jumped... just a guess.
Try: jumper A (jp3?) at CKM and jumper B pulled.

Kixs: some at vcfed have gotten their 287XL to work at 16Mhz but not all.... just saying you may have a very lucky one....

Hi,
JP2 has 3 pins and its set as 2-3.. will have to reassemble and try the other way,, is in a very awkward position with the machine assembled.
in the case i does´t work do you think just soldering a 24Mhz Cristal and halving whit CKM jumper It should work ?

If this JP2 is in the wrong position it will explain why it doesn't work even with turbo OFF as kixs suggested

Nexxen wrote on 2024-11-26, 10:24:

Ernesto22 wrote on 2024-11-26, 03:54:

This is the board's full view picture.. Hope this helps to identify and find some info. It has a place for a fpu dedicated cry […]
Show full quote

This is the board's full view picture..
Hope this helps to identify and find some info.
It has a place for a fpu dedicated crystal...
And the RAM counting picture..

The attachment Screenshot_20241126_004409_Gallery.jpg is no longer available

The attachment 20241126_003137.jpg is no longer available

https://theretroweb.com/motherboards/s/pcchips-m209#driver

You probably have a different version. Not in records.

thanks a lot for this
board layout is very different but bios post is the same but the two last digits. and BIOS options are exatly the same.. I even have the diskette with the same tools.

Ernesto22 wrote on 2024-11-28, 00:09:

Hi, JP2 has 3 pins and its set as 2-3.. will have to reassemble and try the other way,, is in a very awkward position with the […]
Show full quote

Hi,
JP2 has 3 pins and its set as 2-3.. will have to reassemble and try the other way,, is in a very awkward position with the machine assembled.
in the case i does´t work do you think just soldering a 24Mhz Cristal and halving whit CKM jumper It should work ?

If this JP2 is in the wrong position it will explain why it doesn't work even with turbo OFF as kixs suggested

Ahh JP2 has 3 pins. Could not tell from photo. I think if you had a Crystal installed the other position (1-2) could enable it to be the FPU clock.
I think now the FPU is trying to run off the 40Mhz cpu clock for 20Mhz (with CKM jumper) which is probably too fast as you have a early edition 287XL like me with no small SU# and no big print on it like kixs has.
Just a guess...there is also the chance it is dead but doing the 24Mhz crystal is a good idea !