9 Jan
2009
9 Jan
'09
9:03 p.m.
On Jan 9, 2009, at 3:55 PM, Ethan Dicks wrote:
Hence, they're not "weird chips". =) It's the weird ones I'm
worried about.
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 (they
might designate various data or address bits in a different order, but
for RAM it's irrelevant), and are only 0.3" wide (meaning you can use
two 14-pin sockets rather than having to buy yet another footprint). 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.
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? 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)
-Dave
--
Dave McGuire
Port Charlotte, FL