Memory/cache on the 11/70

Ethan Dicks ethan.dicks at
Fri Jan 9 16:59:39 CST 2009

On Fri, Jan 9, 2009 at 4:03 PM, Dave McGuire <mcguire at> wrote:
> On Jan 9, 2009, at 3:55 PM, Ethan Dicks wrote:
>>>  Standard chips good.  Weird chips from the PC world, bad.
>> I'm not advocating the reuse of SMT 128K cache chips, but the 32Kx8
>> DIP chips from old motherboards have a JEDEC-compatible pinout...
>  Hence, they're not "weird chips". =)  It's the weird ones I'm worried
> about.

OK.  I think we are on the same side here ;-)

>> I've seen more than one hobby design that had a 0.6" footprint for a
>> 62256 _and_ narrow pads for a 0.3"-cache SRAM (and even with SMT pads
>> inside that).  It's possible to be flexible for no significant extra
>> effort.
>  That's very nice indeed.

Yeah... the one that comes to mind with three footprints is a
common-in-the-CBM-world hobby add-on that sits in the 6502 socket and
provides up to 32K of RAM and up to 32K of (flash) ROM for use in 8K
PETs, 1541 drives, or pretty much most of the 8-bit CBM line.  It's
great for multiple ROM sets, bypassing C= drilled "upgrade prevention"
holes in 16/32K boards, flaky RAM or ROM sockets, etc.  For the RAM
bit, just pick your footprint and drop in a RAM chip.

>> The DIP cache SRAMs are no longer cheap-as-chips, but some of us have
>> a tube or two stashed away and I sure don't mind using them for
>> non-battery-powered circuits.
>  The JEDEC ones, or the "weird" ones?

JEDEC ones - I don't have the time to untangle wierd ones.

> I see some from time to time, and I
> grab them if they're "standard" enough.  I got a pair of really 20ns nice
> cache SRAMs on eBay last year, Paradigm PDM41256SAs.  Despite their
> seemingly familiar part number, they are 32kx8 SRAMs, not 256kx1 DRAMs.
>  They're in 0.3" ceramic 24-pin DIPs.  I'm saving them for a "pretty" Z80
> SBC that I'll be building soon, on which all chips are ceramic.  (I've
> always had a great love for ceramic chip packages, and I grab useful
> ceramic-packed chips whenever I can)

Nice.  Sounds like it'll have great presentation value.  You have
purple ceramic for the VLSI or just grey?


>           -Dave
> --
> Dave McGuire
> Port Charlotte, FL

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