>
>  ----------
> From:  owner-piclist[SMTP:owner-piclist@MITVMA.MIT.EDU]
> Sent:  Thursday, August 29, 1996 12:30 AM
> To:  Multiple recipients of list PICLIST
> Subject:  Re: Mass Storage
>
> >         I'm using a PIC16c84, and i'm going to need more memory than it
> > offers, I was considering either a floppy drive, zip drive, or
> something
> > to that extent, the simpler the better, any ideas?
>
> Uh, how much more memory?  For under $1/Kbyte, you can add serial EEPROM
> chips quite easily.  (snip)
>
>  -----------------------------
> Problem with EEPROM is 10*6 write cycles typically (for Microchip parts).
> It depends on how often one needs to write. Every 10 minutes would be no
> problem. But every second could be.
>
> What other storage options are open to PIC users for extra memory?
> Philips has a 256 byte static ram chip with I2C. But are there other
> serial static ram chips? One poster suggested using static ram chips such
> as are used in PC cache memory systems, but
> I suspect these would be messy to interface to.

That would have been me. And yes the interface does have its downside. At
minimum 10 pins of I/O and 4 chips (RAM, 2 latches, 1 2-4 decoder)

And you lose every bit of the I/O space. It's possible to recover 16 bits
(8 inputs, 8 outputs) at the expense of another 2 chips (latch, buffer)
and upgrading the 2-4 decode to a 3-8.

Dallas Semi encapsulated the above design into a single chip (DS1380 and 1381
with the 1381 having an integrated lithum cell for battery backup). It gives
2K static ram and a bidirectional 8 bit I/O port at the cost of 10 pins
(8 regenerated). The DS1380 is about $9 in singles. check out

http://www.dalsemi.com

I highly recommend Dallas Semiconductor because they have really taken
the time to deal with folks who need small quantities of their parts. With
an 1-800 number, credit card orders, no minimum, and data sheets online,
one can really cook with their stuff.

All of the above is on the premise of fast parallel access. Now if speed isn't
an issue then it becomes more interesting... The 74X595 is a ideal chip
for addressing lots of I/O bits serially. It's a 3-state 8 bit serial shift
register with integrated latch. Also it's cascadable due to the non 3-state
output pin that holds the last bit of the shift register. The whole job
can be done with 3 of these puppies and 3 I/O bits.

But the original poster was talking about floppies and ZIP drives. I got the
distinct impression that:

A) He wanted a lot of space.
B) The space had to be semi-permanent.

With a low end of 1.5 Megabytes and a high of almost 100 MB, I don't think
that any semiconductor solution is going to be cost effective.

I still think interfacing to an IDE hard disk has the most promise....

BAJ