On Jul 26, 5:01 pm, Flyingtoasteroven
<[email protected]> wrote:
> Your peculiar find has inspired me to do some more digging-- also in
> accessmylibrary, but with a temp acct.
>
> Apparently on or about Nov 1991, they clocked a 68030 at 55Mhz, added
> 128k of 15ns SRAM (replacing 32k of 20ns SRAM) and required 70ns SIMMs
> "The second ingredient in Nexus fx performance gains is the larger and
> faster cache.
It might be possible to identify the destination of the unconnected
wires using the information above. It appears that the CPU and
faster cache are on the add-in card. So, presumably, the wires
needed are probably control lines for the cache, and maybe two address
lines from the memory controller? It would take a lot of circuit
tracing, but I think it would be doable. Probably about 20 - 40 hours
of work, would be my guess.
My approach would be to first trace what the 32K cache is connected to
on the logic board. Get a datasheet for the SRAM chips used and use
that to give some idea of what's what. Address pins must connect to
address lines, control lines to control lines. That kind of stuff.
Once you know what the 32K is connecting to (e.g. are the address
lines direct from the CPU or do they go to an intermediary control
chip?) then you can see how it corresponds to what the 128K cache is
connected to. It may be possible to reason logically from the
difference to determine what's missing. Also, presumably, the broken
wires are connected at one end? That gives a pretty giant clue as to
what they should connect to at the other end.
The other interesting part of this is that fast SRAM is cheap now
days--ranging from $1 for a 256K module at OWC (has the chips which
would take the IIfx to 128K) to a couple of dollars for a 256K or 512K
SRAM chip such as was used with the G3. If the wiring could be
mapped out, it might be fairly easy to make a new cache expander for
the IIfx. It wouldn't be economical (development cost vs. tiny
demand) but it might be fun.
Jeff Walther
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