29 Jul
2004
29 Jul
'04
12:02 p.m.
Hi Jay
Al and another fellow at Monday pizza talked about this.
One could setup using one of the high speed CMOS cache
chips, pic ( or processor of your liking ) and an EPROM.
One can hold the reset signal until you'd transfered the
image to the CMOS ( it would have space for just about
every combination ). One could even use a flash instead
of an EPROM and then add a serial port to download.
Most of the fused ROM's used in the original were in
the 50 to 60 ns range. Most 8Kx8 cache RAM's are in the
20 to 30 ns range.
It sure sounds like a project that can be done.
Dwight
From: "Jay West"
<jwest(a)classiccmp.org>
Ok, I don't know if this is possible, but it would be handy so I'll throw
the idea out and see if the more electrically inclined have any ideas.
My specific issue is the HP2100A, 2100S, and 21MX M/E/F systems. However, I
suspect this problem is present in other machines... DEC, DG, etc.
The loader roms and microcode roms (two different chips) for each system are
pretty much impossible to find. I'd like to make copies of them both for
myself to use in other systems I currently have, and also to have a set of
spares around. In addition, I'd like to make copies for other classiccmp'ers
who may have systems that want/need a particular firmware or loader rom
option. Finally, there are some roms that people have posted images for
online that I'd like to burn myself because I don't have those particular
roms.
Since the blank chips are nigh impossible to find anymore... is it possible
to use something like a PIC chip on a small DIP carrier card, that could be
plugged into an existing loader rom or microcode rom socket and function
just like the "real thing" to the system? Would this be something terribly
difficult to build? A cute twist on this.... extending the idea further....
Put a bunch of NVram or an EEprom on the little carrier card. In the NVram
could be stored multiple ROM images. Then via a switch on the card (when the
system is powered off of course), you could select if the chip was a mag
tape loader rom, or a paper tape loader rom, etc. For the microcode roms you
could switch between FFP and IOP for example. When you wanted to change the
set of rom images in the DIP package, you just hook it up to a serial port
and download to change the available sets on it.
The WCS card for HP boxes comes close to this, but there's no battery
backup, and you can't program it easily with a PC. WCS cards probably aren't
terribly easy to find anyways.
Is this a pipedream? It would allow DEC'ies to have more loader roms they
dont currently have by exchanging images via the net, etc. Not just an HP
thing - but I realize it would have to be a different design electrically to
work on the other machines. I'm thinking of a universal rom with different
electrical interfaces on the carriers perhaps?
Everyone talks about preserving ROM/PROM contents. But if the blank roms are
unobtainium, we need to take the next step.
Any thoughts?
Jay West
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