HSB240 and 68881 co-pro decoder needed

[guus.assmann]

Hello,

 

For some time now, I'm the proud owner of an HSB240 board.

This board has the possibility to add the 68881. This chip, I do have.

But for it to work, I also need the decoder GAL.

Does anybody have this Gal or the Jedec file, so I can program it.

I'dd still need to know the type of Gal as well.

Thanks,

 

BR/

Guus Assmann

 

[guus.assmann]

Well, I got a nice mail from mr Heyer. But he had no info.
So I started myself.

First, there's an 74F20 that has it's output(6) to pin 2 of the GAL.
Inputs on this are A23, A22, A21 and A20 on pins 1,2,4,5 respectively. (Other half F20 not used)
The Gal has it's pin 19 connected to the 68881 CS, with a 10K pull-up.
Gal pins:
1 = A5 : 2 = 74F20-out : 3 = A6 : 4 = A19 : 5 = A18 : 6 = A17 : 7 = A16 : 8 = A7 : 9 = A8\ : 10 = GND
11 = A9 : 12 = NC : 13 = A10 : 14 = A4 : 15 = A12 : 16 = A13 : 17 = A14 : 18 = A15 : 19 = CS-68881 : 20 = VCC
So all I have to do now is enter the I/O into a Gal programming prog and add the equassion.
The latter is simple:
/CS = /74F20 & A19 & A18 & A17 & A16 & A15 & A14 & A13 & A12 & A11 & /A10 & A9 & /A8 & /A7 & A6 & /A5
But making 11 and 13 to 18 inputs may be hard. (Had a problem in the past)

I guess a 16V8 with 7nS will do the trick.
BR/
Guus Assmann

P.S. I will post the results when I'm done.

[guus.assmann]

After a lot of setbacks, I finally managed to get a Jedec file.

It's been made with Hatari emulator and the GABI software from Ralf Zimmermann.

The GAL does give the correct reaction on my testboard.

But in the HSB it doesn't work.

I may have destroyed the 68881, it's been in the socket 90 degrees counter clockwise.

Not sure if it can surrvive this. The Power Supply didn't start.

With the chip seated properly, it still doesn't work, but the Supply starts correctly and the computer runs just fine.

I hope I can find another 68881 or test it in another way.

 

Guus

DEC68881.zip

[frank.lukas]

I think you can not destroy the FPU with only Hi or Lo over the CS Input ...

 

One Time I put in the wrong way the FPU and it went very, very hot. After cool down I put it in the right way in and it works fine.

[guus.assmann]

Today I've successfully tested the HBS240 with an 68881 FPU.

When using Gembench 3 or 4 the FPU is detected and I get the expected values for the calculations.

So this confirmes that the GAL is ok. I've use a 7nS device.

 

BR/

Guus Assmann