PDP-8: (and others) anyone tried NVRAM simulation of hard drives?

From: Ethan Dicks <erd_6502_at_yahoo.com>
Date: Fri Jan 31 18:58:18 2003

--- David Gesswein <djg_at_drs-esg.com> wrote:
> From: Ethan Dicks <erd_6502_at_yahoo.com>
> >One thing that has been slowing me down is
> >deciding how to attach a modern device to an -8/L or -8/i...
> >
> I would recommend getting the DEC compatable cards for Dougless
> Electronics to plug into the 8/I and wiring them to another circuit card.

That was one of my options. Any ideas about what to use for the
cabling? I've seen three types used in real DEC hardware - coax
(with the lowest propagation delay and longest bus lengths possible),
mylar flat cable, and stranded-wire ribbon cable. Obviously, a roll
of ordinary ribbon cable is probably going to be the cheapest and
easiest for hobbyists to work with. I suppose with only one device,
and in the same cabinet, it shouldn't pose too many problems.

What would you estimate the entire harness to run? $100?

> With a bank of transistors you can convert from the negative bus to TTL
> and put a small FPGA/CPLD on the board to do all the work.

If I were more comfortable with FPGA/CPLD design, I would probably go
that route. My expertise is more in microprocessors; I was contemplating
throwing an MC68000 on the other end of the bus since I have extensive
stocks (dozens of tubes), a large assortment of hardware debugging tools
(code trace analyzers, a Flike 9010A, etc.) and lots of expertise.

I was thinking of recycling the COMBOARD design - 1/4 of the memory
map is "shared memory" - there is a circuit between the 68000 and
the host bus that initiates DMA cycles when the 68000 reads/writes
to it. I have used a COMBOARD to test the RAM in a PDP-11/03 via
this shared memory interface.

Not the most efficient way to do it, but with the tools/skills I have,
it's how _I_ would do it. Naturally, if someone else does the engineering
work, I can *build* stuff that I didn't design.

Received on Fri Jan 31 2003 - 18:58:18 GMT

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