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PICList Thread
'Floppy Drives and pics'
1997\08\04@120922 by Jim Main

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Has anyone ever hooked up a PIC to a 3.5" floppy drive?  I tried a
search on the web, but couldn't find technical details on floppies
anywhere...

Jim
--
Jim Main

1997\08\04@163550 by Martin McCormick

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Jim Main writes:
>Has anyone ever hooked up a PIC to a 3.5" floppy drive?

       I was asking questions about this several weeks ago.  It doesn't
appear that a PIC is a good choice to either control a floppy disk drive or
use a floppy as a storage device.  the serial data rate from the read head
would be around 500 KB/S (MFM) which would keep the PIC pretty busy just
reading data.  There is also nowhere near enough RAM available to store
a track's worth of sectors in a buffer, assuming the PIC could keep up with
the stream.

       PIC's are nifty little controllers, but their talents wouldn't be
suited to the demands of the job in this case.

Martin McCormick WB5AGZ  Stillwater, OK 36.7N97.4W
OSU Center for Computing and Information Services Data Communications Group

1997\08\05@062250 by Jim Main

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In article <PICLIST%spam_OUT97080416355004TakeThisOuTspamMITVMA.MIT.EDU>, Martin McCormick
<.....martinKILLspamspam@spam@DC.CIS.OKSTATE.EDU> writes

>>Has anyone ever hooked up a PIC to a 3.5" floppy drive?
>
>        I was asking questions about this several weeks ago.  It doesn't
>appear that a PIC is a good choice to either control a floppy disk drive or
>use a floppy as a storage device.  the serial data rate from the read head
>would be around 500 KB/S (MFM) which would keep the PIC pretty busy just
>reading data.  There is also nowhere near enough RAM available to store
>a track's worth of sectors in a buffer, assuming the PIC could keep up with
>the stream.

So couldn't you just read the data straight into external ram and let
the pic worry about it later?

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).

I know its a bit of a hammer to crack a walnut, but the advantage is
that these drives are very inexpensive..

(still looking for pinouts, details etc if anyone knows where to find
them)

Jim
--
Jim Main

1997\08\05@064207 by Lee McLaren

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Have you considered using a dallas touch button, you can get 64kb
versions and the software to use is very easy to write and no harware
required only one pin on the pic.

Lee McLaren


Jim Main wrote:

{Quote hidden}

1997\08\05@112930 by Eric van Es

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Jim Main wrote:

> Has anyone ever hooked up a PIC to a
> 3.5" floppy drive?  I tried a
> search on the web, but couldn't find
> technical details on floppies
> anywhere...
>
> Jim
> --
> Jim Main

I was searching for ways to use just the
stepper from floppy drives (5.25") ( I
thought 3.5" was a *stiffy*?).
Try these :
http://www.hut.fi/misc/electronics/circuits/diskstepper.html

http://jewel.morgan.edu/~tmalone/dskdrv/dskdrv.html

G ' luck!

eric
--
eric van es
Mailto:EraseMEvanesspam_OUTspamTakeThisOuTilink.nis.za  WWW:
http://www.nis.za/~vanes/
Cape Town, South-Africa
Looking for TEMPORARY/HOLIDAY
ACCOMMODATION?
http://www.nis.za/~vanes/accom.htm

1997\08\05@115510 by Peter Baines

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>
> I was searching for ways to use just the
> stepper from floppy drives (5.25") ( I
> thought 3.5" was a *stiffy*?).


Hmmmm a 3.5"  Stiffy...... have you considerd prosthetics :))))))


Cheers Peter..........

1997\08\05@124035 by Harold Hallikainen

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On Tue, 5 Aug 1997 10:58:34 +0100 Jim Main <jimspamspam_OUTEWCOMM.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

1997\08\05@134954 by Tim Kerby

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Hi
I think you can read a bit at a time, there is some sort of data rate
control that a floppy has although I dont know what.  It seens that certain
programs on the PC can read a byte at a time using this system.  For
pinouts check the hardware book that is great as a windows help file or
html at http://www.blackdown.org/~hwb/hwb.html


Tim


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1997\08\05@150513 by Mike Keitz

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On Tue, 5 Aug 1997 18:40:18 +0100 Tim Kerby <@spam@tim.kerbyKILLspamspamUKONLINE.CO.UK>
writes:
>Hi
>I think you can read a bit at a time, there is some sort of data rate
>control that a floppy has although I dont know what.  It seens that
>certain

A floppy drive is an entirely "dumb" device, it is just an amplifier and
analog processor hooked to the read-write head on the disk. Data comes
out raw at approximately 250-500 Kbps depending on the disk format.  The
data comes out in pulses about 500 ns wide.  The timing between the
pulses encodes the data according to a coding scheme known as MFM
(Modified Frequency Modulation).  As I remember, a zero bit is an early
pulse and a 1 is a (1/2 bit) late pulse, except a 0 that follows a 1 is
no pulse.  This guarantees that pulses are never closer than one bit time
to each other and never farther than 2 bit times from each other.  The
exact rate varies a little with the motor speed (relative to the speed of
the motor in the drive that recorded the data).  There is no "data rate
control".  The controller needs a PLL or similar circuit to track data
rate variations.

Each sector on the disk has about 4 bytes of header which confirm which
track, and sector, and head is about to be read.  These headers start
with a special byte which violates the MFM code.  After the header there
is a short pause then the data (512 bytes on a PC), which also starts
with a MFM violation for synchronization.  The pause is very important as
it gives the drive time to change from read to write mode.  The data in
the gap will be garbled because it is partially written.  There is also a
gap after the sector's data before the header for the next sector.  This
is to allow for the motor in the drive to be a little fast without
overwriting the next header.  The headers are written only once, a whole
track at a time, when the disk is formatted.  If the drive is ever in
write mode when the head goes over a header, the sector will become
unreachable and the disk will need to be reformatted.  The drive also
puts out a pulse once every revolution of the disk.  This is used only to
(a) put the sector zeros at the same place on every track during
formatting and (b) time-out an unsuccessful search for a sector header
after several rotations.

Reading a few bytes at a time into a device which doesn't have enough
memory to hold a whole sector is feasible (though not very practical,
since leaving the motor on for a long time will wear out the disk).   But
partial writing isn't, because it takes several bytes worth of time to
change from read to write mode or back again.  Trying to start or stop
writing in mid-sector will garble the data.

Floppy controllers for PCs are now integrated into one chip, which has an
8-bit bus interface and needs only a crystal to work.  These chips often
include serial and parallel ports as a bonus.  But thy don't have any
RAM, so the system needs to take or supply about 40K bytes per second to
it in a quick burst once the desired sector comes up.

1997\08\05@162247 by Steve Smith

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In a message dated 05/08/97  15:56:52, you write:

<<
>
> I was searching for ways to use just the
> stepper from floppy drives (5.25") ( I
> thought 3.5" was a *stiffy*?).


Hmmmm a 3.5"  Stiffy...... have you considerd prosthetics :))))))


Cheers Peter..........
 >>
Maybe if using a PIC then Prosthetics Inferring Circumcision ?

1997\08\05@225011 by Mailing List Account

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       I've got several Z765A Floppy Disk Controlers (which I believe
are compatiable with the 8272A and NEC uPD765 used in PCs), the datasheet
says it can do single and double density.  Is high density supported by
these chips?  Shouldn't it be possible to interface these with a PIC?
They're only $0.99 USD.

                                               Philip Lalone

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