New idea HD for C=
Date: 1999-09-03 21:30:17

Hallo allemaal,

Here is another idea for attaching an "harddisk" to your C=. But to refresh
your mind I give you a history of older idea's:

Connecting an IDE to your C= thru an interface
      You need to rewrite the original Kernal. The problem is that a lot of
      PRGs (like GEOS) bypass the Kernal but by doing so they cannot see the

Connecting a PC to the C= thru a X1541-cable or an IEEE-equivalent.
      In this case it all depends on how well the SW can emulate one of
      original C= drives. But AFAIK there isn't one available yet.
      (Frank ????)

Connecting an IDE-drive to a 1541
      The idea is to addapt the above interface so it can be used by the 6502
      in an 1541-drive. Then you have to change the Kernal. Problems: 1)
      there is no listing INCLUDING comments etc. available. 2) Even if you
      have the listing, it is very tough material to understand. 3) what
      about PRGs who directly address the 6522 used for the transferring the
      data from/to the floppy

Connecting a PC thru the printerport to the 1541
      The basic of this idea is to get rid of the floppy and some IC's,
      mainly the array 3255272-01, and use the above mentioned 6522 as
      communication port with the PC. 
      Advantage: Less soldering then the above idea. Problems: the same.

Now my latest idea. The essence is the same as the above idea: get rid of the
drive and some electronics. Then connect a PC to the 6522 thru an interface. 
The idea is to let the PC behave like the original floppy and electronics. So
if the PC sees the 6522 giving signals for the original steppingmotor, it
adjusts the SW-pointer which tells the program which track the 'drive' is

I do not know what kind of interface to use. I'm thinking of using a printer-
port but I/O-operations of an Intel-machine need a lot of time: 0.5 uSec.
Another option is to rebuild an old LPT-card so it is addressed by a memory-
read/write. Then things can be speed up to 8 MHz or more.

There are two ways of changing "floppys":
1)    We give a command to the PC which on its turn searches for the new
      "floppy" and then manipulates the "Write-protect"-input so the 1541
      thinks the floppy has changed. Needs an extra keyboard and monitor for
      the PC.
2)    We have to change the Kernal of the drive. We at least need to add a
      command so we are able to change a "floppy". PC works stand-alone.

I also have some thoughts about how deal with the data. The moment a real
floppy is formatted, a stream of bytes is send to the ports of the 6522 at
certain intervals. Writing to a floppy is first searching the sector by
reading the contents of the correct track and then writing the data. IMHO the
only thing we have to do is read/write the data at the same interval. The
only difference with a real system will be that the start of reading a real
floppy will be random somewhere in the track and I always will start at the
first sector.
The only difficulty will be determing the interval, the rest seems just to be
reading/writing a stream of bytes: We even do not have to know what kind of
information they represent.

I would like to know your opinion, comments etc. about this idea. Thanks.

Groetjes, Ruud

PS: Is it "a 1541" or "an 1541" ? :)

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