On Tue, 5 Aug 1997 10:58:34 +0100 Jim Main <jim@EWCOMM.DEMON.CO.UK>
writes:

>
>I thought it'd be a good idea to incorporate a floppy drive into
>various
>bits of pic-controlled equipment as a software upgrade path (obviously
>only for flash pics of which there'll hopefully be more available in
>the
>future).
>


        Seems that the cheapest way to do a firmware upgrade on a PIC is
to replace the chip!  If you want to make this a user upgradable product,
you could go with a PIC on a small card accessible from outside, or just
put the PIC in a ZIF socket.
        On disk drives... about 10 or 15 years ago I was faced with
adding disk storage to a 68B02 product.  the Commodore 1541 disk drive
had a built-in operating system and only required three or 4 wires to
communicate with it.  So I captured a bunch of the data passed back and
forth between a VIC20 and the 1541, decoded it, then  wrote 6800 assembly
to emulate it.  The product had a Microsoft Basic interperter in it, so I
added words for SAVE, LOAD, and DIR.  Also added SBCMD that would send
any other serial bus command to the 1541.  That was used for deleting
files and formatting disks.  It worked out pretty well, though it wasn't
very fast.  Still a few hundred of those systems out there.


Harold