2 Mar
2012
2 Mar
'12
11:04 a.m.
Reading the following, I have to make some comments:
On Thu, 1 Mar 2012, jim s wrote:
i do have one of the Diskferret board sets, for this
reason. And I'm one of
the lame ones who has not had time to use it as yet. However I have
confidence that it will provide what I want, not only for the floppys it was
working with when I bought it, but with hard drives. I have several 14" SMD
drives which may come into play, and perhaps in an ideal world some drums to
digitize, and this is an ideal open tools to do so with.
I think the DiscFerret doesn't help with SMD drives as they have a
somewhat intelligent interface and pure uncoded, i.e. NRZ, data. I have
just built a "simple" interface for a PC on an ISA prototyping board
(with wire-wrap!) because I have the need to get the data off from several
SMD drives from an unknown machine with an unknown controller. Essentially
you need a lot of RS422 drivers/receivers (everything on the A and B cable
is differential!), some registers to control the bus and tag lines, and a
means to shift the bits into a buffer. Per se, it's not very difficult as
you have a nice read clock signal along the data signal on the bus. Just
read in all bits from index to index, and analyse that bit stream in
software. No need for a PLL or decoder whatsoever.
I doubt that Phil will be coming to my LGP30, but
digitizing the drum's
contents would not be out of the question. I would be able to do the
engineering with him, hopefully should that happen in the future.
The DiscFerret won't help with this drum either. Speaking of experience
(having two working LGP30s), you don't really need to digitize the drum if
the machine (or more exactly, the matrix drivers and read FFs) are
working, just hook up your logic analyser or whatever to the read FF and
select the desired track. Your read clock is the main clock (137 kHz for
the European version). Since there's no index pulse you need to read the C
register together with the two clock tracks S2*/S3 to get the number of
the next sector. The word mark is the sign bit. ... But you really only
need to do that if you absolutely can't get your LGP30 working.
When we got our first LGP30, before the machine itself was operational, we
had dumped the drum with a Dolch logic analyser and found a mostly empty
drum with some code fragment somewhere in the middle. We used some simple
TL084 opamps to digitize the signal and feed it into the pod.
Many years later we discovered that this is what is left after running the
LGP30 acceptance test.
Christian