[sdiy] Old memory chips for edp spider - IM6561CN or IM65X61JN ?

[dj hohum]

With minor modifications you can use the 5101 which is easier to find.
The following is a conversion guide found on the web. Pay attention to
the schematic because the second cs line may not actually be in use.
If that's the case, you simply need to cut the trace and wire the line
to ground.

hope this helps.

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This allows you to use a 5101 instead of a 6551-9 CMOS chip.
The 6551-9 is almost impossible to purchase, but the 5101 is readily
 available at Jameco Electronics.

The 9551 is a VERY similar cousin to the 5101 CMOS static RAM.  Both are
256x4 bit.  Only difference?   The second chip select line (CS2, pin 17)
is active low on the 9551, and active high on the 5101.   The fix to use
the 5101 is to cut the trace on the top of the board, coming from U5 (a
74LS32), pin 8.   Jumper the U5 side of your cut to an unused inverter
gate input (7404), and then send the output of that inverter gate back
to the other side of your cut.   I used the pins 11 (input) and 10
(output) of IC24.   Thats a spare inverter that was nearby.   This will
invert the CS2 line, which is what you are looking for.
------------------------------------------------------------------------------------------------------------------

On 6/18/07, Tom Corbitt <tom.corbitt at gmail.com> wrote:
> Well,
>
> The hm6551 should be a drop in replacement for it, but the last
> version they've got active sure isn't cheap. Looking at the datasheet
> it shouldn't be that hard to just wire in a larger newer cmos chip and
> just ignore the extra memory (I'm thinking of a smt version soldered
> on a dip socket kind of thing)
>
> http://www.intersil.com/cda/deviceinfo/0,1477,HM-6551FWDSLASH883,00.html
>
> Tom Corbitt
>
> On 6/18/07, Julian <julian at 22host24.com> wrote:
> > My spiders, upon testing, are as most spiders seem to be - dead.
> >
> > The problem has been traced back to the memory chips (not by me mind) but
> > the person working on them has had no luck in finding suitable
> replacements.
> >
> > So, anyone got a big bag of these knocking about ; ) or know a man (or
> shop)
> > who does?
> >
> > Im in england, if that makes any difference to anything?
> >
> > Thanks, Julian
> >
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