RE: Repairing a SFD-1001 (8250/LP, 8050, 4040, 3040, 2040)

From: Hoffmann-Vetter, Martin <>
Date: Fri, 12 Aug 2011 17:54:02 +0200
Message-ID: <002501cc5908$0f6bdf80$>
Hello Jim,

> I was thinking I could feed the CS1,2,3 lines into the '138 with
> jumpers and pullups on the '138 input lines.  Then, 8 jumpers to
> select which combination was needed for the JEDEC /OE line.  That
> would handle inversions of any line, but each of the CS lines needs 3
> states:
> connected to nothing
> connected to '138
> connected to JEDEC pinout.
> So, I'd need 3 2 way jumpers and 8 1 way jumpers to handle every
> combination.

Or you use a 151. But 8 jumpers at the inputs D0 to D7, wire the 3 chip
select signal to A, B and C und the output signal W to the chip select of
the eprom. The strobe input must be grounded.
Now you can put 1 or more jumpers and programm the used chip select signals.
So you can use it for the 2332 (two jumpers) and 2364 (four jumpers).

The other way is to use a comparator eg. 688. You wire the chip select
signal to A0, A1 and A2, put B0, B1 and B2 with pullups and put an 3 pin
jumper to connect to ground or Ax. The output is the chip select signal for
the eprom. So any jumper position has 3 state:
* don't care (connected Ax and Bx for a logic 1, always true)
* must be 1 (is only true if Ax is logic 1) and
* must be 0 (is only true if Ax is logic 0).

The last idea can be expanded to a 2308 or 2304 (does the last one exists?)
or to use other signal to generate the chip select from the eprom, too.

If i remember, the 2308 has only two cs at pins 18 and 20. Pins 19 and 21
are not connected! The MC68x308
.pdf page 2-137) has all four pins with the option for chip select.


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Received on 2011-08-12 16:00:03

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