Harold M Hallikainen wrote:
>
> >On Thu, 17 Dec 1998, Dave Celsnak wrote:
> >
> >> Hello,
> >> Does anyone have experience interfacing a PIC to a Multi Media Card
> >from
> >> SanDisk?
> >>
> >> I am very interested in using a 4meg Flash memory card from them.
> >
>
>         Which gets me thinking (always dangerous!)...  In my last post, I
> commented on my plans to add a 128 Kbyte RAM chip to a product to hold
> user data.  Now, the user would, of course, like to safeguard that data
> by having SOME sort of removable storage.  Removable memory cards are
> expensive (compared to a floppy disk), and may not be a whole lot easier
> to interface to.
>         There was some previous discussion on the list about interfacing a PIC
> to a floppy drive.  At the time I thought that was stupid!  Who would
> want to use a floppy to save the contents of 200 or so bytes of RAM in a
> PIC.  Now, of course, with 128 Kbytes of external RAM, I DO see some
> value in external storage, and the floppy is looking nice.  The disks are
> incredibly cheap; the drives are incredibly cheap.  All we need is a
> version of DOS on a PIC so you can dedicate a PIC to driving the floppy,
> then talk to that PIC through its serial port.  Anyone done ANYTHING like
> this?
>         About 15 years ago I designed a 6800 based product where I needed
> external storage.  The first units used good old audio tape.  I then
> wrote code to talk with Commodore (as one of my students pronounced it:
> Commode Door) disk drives.  Those were kinda neat since they had the
> operating system built in.  You just had to figure out how to talk thru
> their serial bus.  I did that and sold a ton (a small ton) of products
> that are still using the Commodore drive.  Something like that with the
> PIC would be pretty neat.
>         It would be CHEAP code you could drop into a PIC to make it a serially
> controlled disk drive controller chip that writes IBM format on 3.5 inch
> disks.  Anyone written that?
>
> Harold
>
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  I'm thinking of making a solid state floppy drive, with something like
an Atmel AT45D081 (8 megabit i.e. 1 Megabyte) flash disk, and an
AT45D041, so I can bring up a computer without an actual floppy disk
drive.  (I have BAD luck with floppy disk drives, they seem to go bad
often enough that it's a constant problem for me.)  [Also there is no
way for a virus to write itself on there, that's a thought too!  <G>]
Simulate multiple floppies on one Flash bank with a rotary switch,
perhaps.  Haven't started that yet, doing other things first.

  These Atmel chips are paged, pretty tiny (SOIC-28 etc.), fairly
inexpensive (~$10 for the 1 MByte chip), fast (10 MHz data clock),
7-wires total (Including Vcc etc.), and run off 5 Volts (There are 3.3V
versions.)  The newest product in this line is the AT45D161 (2 MByte)
chip, same packaging.  You could easily just simulate a 720k floppy disk
off one AT45D081, with spare room <G>  There is a pair of page-size
buffers, 264 {or 528 for the D081} bytes each, in these; you can use one
or both as scratch data space or use one or both for I/O to the flash
RAM.  Use the extra bits for ECC or the like.

  Could stick a couple of these on a PC board, add 5 SMD Zeners or
protective diode bridges as needed, solder the PCB to a DE-9 connector,
pot it all inside a shell, and make a pretty small secure data holding
device that could be carried away at will.

  Using the 24LC256,  you would have to use quite a few 32k devices for
a floppy sized device (45 or 46!);  The same DE-9 connector idea should
work readily for 128k, you'd just need 4 SOIC-8's on a PC board.

  Mark, mwillis@nwlink.com, hoping a 24LC2048 is coming out soon <G>