3 Apr
2002
3 Apr
'02
6:27 a.m.
Having the drivers is important. I've looked in vain
for the 75xxx series chips described in the famous
1976-ish Byte Magazine article on core memory that has
been mentioned before. Without those, its a heck of a
lot of discretes, and there's no way around it. Too
bad, because I have some really nice core memory with
the diodes only that deserves to do more than hang on
a wall. I also suspect that because of all of the
unknowns involved regarding the magnetic properties of
the core that you use, the way to go about it is to
put a lot of pots on a single driver/receiver setup,
tweek em to the middle, and repeat. My understanding
of core is that there are thermistors involved also,
and that core had a very narrow range of temperature
operation. There were even programs designed
specifically to cause "hot spots" in the core in order
to test it (you'd have to know the physical layout of
the core to pull this trick off).
--- Joe <rigdonj(a)cfl.rr.com> wrote:
Bill,
You're a man after my own heart! I've been
thinking about this for some time. I once had some
NICE small core planes (16k I think) out of a HP
communications analyzer and I think they would have
been just about perfect for this. I had too many
other projects at the time so I sold them but I know
where there are some more analyzers so I may grab
them and swipe the core from them. I found the
service manual for the analyzer so I had the pin out
for the entire machine including the core. (I still
have it). IIRC the core module was about 5 inches
square and had all the drivers and sense amps on it
so that might make things easier. However there are
some things that you have to do with core and I
don't know if they handled in hardware or if the OS
had to take care of it. For example, reading core is
destructive, that is it erases the contents so you
have to store the contents back into it before you
do anything else (unless you don't care if it's
lost). That seems like it wou!
ld be easy enough to do in HW but I don't know if
that's what they did.
Joe
At 11:41 AM 4/3/02 -0600, you wrote:
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Right off, let me say that I know next to nothing
about the realities of
using core memory. I only know that it looks like
pretty cool stuff to
play with. Would I be completely off my tree to
try to build a core
memory interface from scratch, assuming I had a
pre-strung core frame with
all the cores and wires intact? When I say
"interface", I mean basically
something that will let me talk to the core from a
PC or from my
recently-completed Mark-8 using TTL or CMOS
levels.
If I have a 64x64
frame, would I just need something on the order of
256 driver transistors
(one to drive each of the X and Y wires in either
direction) plus some
kind of op-amp or comparator circuit to monitor
the
sense wire (is there
just one of these per frame?) and determine
whether
or not a bit has
flipped during a read pulse? Or are there all
sorts of ghosts and goblins
lurking in core memory that I don't want to
confront?