HSB240 coprocessor 68881 info needed.

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guus.assmann
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HSB240 coprocessor 68881 info needed.

Post by guus.assmann »

Hello,

My HSB240 has two empty sockets, one for an 68881 and one for the decoder this needs.
So I would like to fill the sockets and already have the 68881.
All I need now is the decoder Gal or the Jedec file for this.
Does anybody have this available?

BR/
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frank.lukas
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Re: HSB240 coprocessor 68881 info needed.

Post by frank.lukas »

Try to find Mr. Neumann or Mr. Heyer and contact them ...
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Re: HSB240 coprocessor 68881 info needed.

Post by Greenious »

Actually adding a FPU is not very difficult, if you can trace what signals goes to the decoder GAL, it should not be very hard reverse engineering it.
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guus.assmann
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Re: HSB240 coprocessor 68881 info needed.

Post by 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.
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Re: HSB240 coprocessor 68881 info needed.

Post by 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.
DEC68881.zip
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Guus Assmann
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Re: HSB240 coprocessor 68881 info needed.

Post by guus.assmann »

Today, I successfully tested the HBS240 with an 68881 processor.
Gembench 3 and 4 do give the expected high speed results for "flooting point math"
Sysinfo doesn't see the processor.

Anyway, this test confirmes that I got the Gal right. I've used a GAL16V8 with 5nS.
And I guess the clock to the FPU is 16Mhz. Maybe I'll overclock it as well. Just because it can be done.
BR/
Guus
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