On Mon, 21 Dec 1998 14:05:17 +1300, you wrote:

>25 years ago (!) or so we played with the SWTP Motorola 6800 based
>systems and similar and did quite a lot of work on the low level
>floppy control software - not very hard once you get into it. We used
>the 1771 floppy disk controller and with it the speed of the 6800 was
>adequate. While you may be able to do the whole thing sans controller
>(a Scenix would help :-)) you would certainly need a certain amount
>of analog interface cctry. I think that using a modern floppy
>controller IC would GREATLY reduce the effort. The 1771 is long long
>dead but I assume that the single chip solutions I see on modern I/O
>cards have the same basic interface and abilities plus, probably, a
>sector buffer. If so the PIC would not be speed constrained at all
>but would still need a (probably) 8  or 16 bit interface. A floppy
>drive presently costs about $NZ30 (?$US15?) and stores 1.44MB (more
>in non-std formats) and apart from the nasty 12v/5v supply needs (but
>only while working) would be a nice solution in many applications.
>
>AFAIR the hardest problem with the 6800's was writing a track while
>formatting as this had to be done on the fly at full diskette data
>speed. The track image was written into RAM and read out in real
>time. A small PIC would not have enough memory for this approach.
But as most of the track data is predictable & fixed, a PIC is
probably fast enough to generate it in real-time, inserting the
appropriate values into the sector headers.