CP/M on an Apple II ?

Chuck Guzis cclist at sydex.com
Sat Oct 8 11:30:05 CDT 2005


>The format from that controller was bizarre enough I don't know if there 
>was any way
>to read them on the IBM PC's disks.  Maybe something like the copy 2 
>option board
>might read the data and store it. does 22/disk read those?

22Disk does not handle them.  Internally here, we use an early Microsolutions Match Point card in an old PC XT with a special version of Uniform to handle Apple II CP/M transfers.  The Match Point also comes with some tools to handle Apple DOS.   The MP will not work in anything much faster than an XT.   I believe that there was another product called "Blue Lightning" or some such to handle those diskettes, but I've never run into one.  

The Apple II recording format is a gutless wonder (like Apple II video), heavily using the CPU to read and write disks--and very dependent on the 2 microsecond CPU clock.  The diskette controller is really nothing more than a  6309 ROM, a 74LS323 shift register that forms a state machine, a 74LS259 latch for drive control and a l and a little glue.  The disk controller card also contains a 6309 boot ROM  

In the days when an LSI floppy controller OEM-ed out at $40-50, it was an interesting low-cost solution.  The data representation is essentially a sort of group code--and there were two versions of this code--DOS 3.2 (5/8) and DOS 3.3 (6/8).  A 3.2 disk contains 13 256 byte sectors per track; a 3.3, 16.

The big weakness in the Apple II disk was the lack of really good error checking.  A simple one-byte arithmetic checksum was used in lieu of a CRC and I've personally experienced corrupted data flying by without being diagnosed.   

I believe that the Apple /// subsumed much of the Disk II controller into a single LSI IC, named the IWM (Integrated Woz Machine) and that some of that logic was carried into the early Macs.

If you're looking for a good no-nonsense book on the innards of the IIe, try to find Jim Sather's book "Understanding the Apple IIe" (Quality Software).  Long OOP, it's one of the better references.

I believe that the Option Board will copy Apple II diskettes, but won't deciper them.

Cheers,
Chuck
  





More information about the cctech mailing list