USB Universal Floppy Disk controller

[Philip Pemberton]

In message <1110586962.6194.110.camel at weka.localdomain>
          Jules Richardson <julesrichardsonuk at yahoo.co.uk> wrote:

> > Why not stuff it all in a CPLD? Maybe create a logic-only version too...
> 
> Well personally I prefer logic-only because I know I'll have the parts
> here, plus I don't have any sort of programmer for making more exotic
> things (ok, so I do have an ancient PAL/EPROM programmer, but without
> manuals I've only ever figured out the EPROM side of it :)

The Altera ByteBlaster and Xilinx Parallel Download Cables are literally
three-component devices - a DB25 connector, a 74LS244 and an IDC header. Plug
the cable into the target board, apply power, run the downloader, hit
"Program", then wait a few seconds for the fuse data to download.

> But also I think that keeping it simple (and understandable) should be a
> goal to enable it to buildable by anyone with a few electronics skills.
> If it means it encourages more people to build it and back up classic
> media, it's got to be a good thing :-)

Only problem is, you might not be able to get TTL logic chips up to the
necessary speeds.

> > 70nS SRAM should work fine, and most SRAM is pretty cheap too. I've got a
> > 512kbit here that cost about £4 and is rated to 70nS IIRC.
> 
> OK so four of those would be enough. That's not *too* costly I suppose,
> although it probably makes it enough for people to think twice about
> it. 

Not to mention the fact that the output from a floppy drive is 1-bit binary.
Adding a 74LS164 shift register would mean you could use a slower RAM at the
expense of slightly more complicated logic and data decompiling.

Writing to disc would also be a very useful feature, lower priority than
reading of course. USB Option Board anyone?

> I still like the idea of SRAM from old PC motherboards; didn't they
> normally have 64 or even 128KBytes? Free then; with other parts costs
> it'd probably make the whole thing do-able for a fiver or so (more with
> a few frills like a case, PSU etc.)

I've got a TAG RAM here from a Pentium board and it's only 16k. I'm still
trying to find a few more of them...

> Yeah, I bailed on IDE for PC systems about 8 or so years ago and have
> only ever used SCSI since. It's nice having the DVD drive, CDROM, DAT
> etc. up on the desk and the rest of the machine tucked away underneath. 

I haven't seen any SCSI DVD writers (or readers for that matter) for ages. I
think a few of the first writers were SCSI, but now they all seem to be
IDE/ATA.

I did have a SCSI card in my RiscPC, but I replaced it with a 100BaseT LAN
card, seeing as I wasn't using the SCSI (no SCSI devices to use with the
card).

Later.
-- 
Phil.                              | Acorn Risc PC600 Mk3, SA202, 64MB, 6GB,
philpem at philpem.me.uk              | ViewFinder, 10BaseT Ethernet, 2-slice,
http://www.philpem.me.uk/          | 48xCD, ARCINv6c IDE, SCSI
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