28 Jan
2014
28 Jan
'14
9:56 p.m.
On Jan 28, 2014, at 4:04 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
It's been a logn time since I've been insdie a
1541, and tghere are at
least 2 main verisons of the main PCB. THe older one used anumber of
small chips and a ROM for the data encodign/decoding, the later one
(qhich ahs at least 2 sub-versions) used a 40 pin custom IC.
Needless to sya that custom IC is not goign to be available.
Perhaps not. I got a copy of "The Anatomy of the 1541 Disk Drive" at
my last vintage computing event with my local group. I should really
leaf through it some time. For those of you who can and will grok
PDF, though, it seems to be available online here:
http://www.jamtronix.com/files/c64_docs/anatomy_of_the_1541_disk_drive.pdf
It covers both the hardware and software (both ends) of the drive,
including a commented listing of DOS 2.6. Not a bad book.
I don't think the 6502 is still beiugn made as a
40 pin DIL chip, is it?
There are plenty of them around, thouhg. Some of the TTL parts fro the
first verison fo the board may bbe no logner maide, but again, gettign
them as NOS is not hard.
The NMOS versions are no longer made, but the Western Design Center
(the group that split off from MOS to make the original 65C02) still
makes a modern version of the 65C02 in 40-pin DIL that, as far as I
know, is a drop-in replacement (at least as much as any CMOS part can
be a drop-in replacement for TTL-interfaced NMOS parts). It still
retains the SO pin, which my fuzzy recollection says was actually used
by the 1541 firmware (and I've never seen it actually used anywhere
else, though it's a neat idea).
So I think, if tyou wanted to, you could ake the
controlelr board using
at orst NOS parts, and close equivalents, like EPROMs raehr htan ROMs I
also think, withoug trying it, you could fit the entier controlelr board
into an FPGA. Whehter you call that a 'clone' I don't know, It does the
smae things, it's the same design. But to me it's nto the same circuit.
You could easily fit the entire controller board into even a very
small FPGA and interface it to everything with appropriate level
conversion ICs. A lot of people might consider that "cheating",
though, and it certainly seems like it might violate the spirit of
the exercise, depending on what your goal is. Developing it with
separate 6502, 6522s, RAM and ROM ICs would certainly be a much
more interesting project, with a cooler board to show off at the
end of it.
But, as I and others have said, the mechanicals are the problem.
If you wanted to be in the business of manufacturing replacement
controllers for the 1541, you could do that, but it seems like a
rather small market. You could also do a halfway solution, that
made a disk controller for, say, PC-interfaced 5.25" and 3.5"
drives that would work on actual floppies, just not the original
ones. It's rather unlikely that you could make that work with
the original ROM image, but not entirely impossible. And it would
be kind of silly.
- Dave