Re: Apple ][ plus 13 sector! Problems...

["Bill Garber" <willy46pa@comcast DOT net>]

"David Empson" <dempson@actrix.gen.nz> wrote in message
1gh4bdp.1ktjcxzfh4v2mN%dempson@actrix.gen.nz">news:1gh4bdp.1ktjcxzfh4v2mN%dempson@actrix.gen.nz...
: "Bill Garber" <willy46pa@comcast DOT net> wrote:
:
: > "Bryan Parkoff" <bryanparkoff@nospam.com> wrote:
: > :     It is what I understand that there are two different
sequencer logic
: > : PROMs.  First is to use 9 bits that it can only have one
zero while
: > : second is to use 10 bits that it can only have two zeros.
It is why 13
: > : sectors use 9 bits while 16 sectors uses 10 bits.
: > :     Do you have 13 sector PROM that you can spare?
: >
: > The firmware can handle how many zero bits to look for.
: > State machine only does what it's told to do.
:
: The state machine is different.  The 16 sector upgrade
consisted of two
: chips: PROMs P5A and P6A, one of which is the logic state
sequencer, and
: the other is the boot firmware.
:
: The 16 sector version of the logic state sequencer is able to
read and
: write 13 sector disks, but not the other way around.
:
: According to Inside the Apple IIe, there were changes in the
read logic
: to improve the reliability of reading 16-sector data.  I expect
it
: changed the timing tolerances to cope better with two adjacent
zero
: bits.
:
: Inside the Apple IIe has a full listing of the DOS 3.2 and 3.3
versions
: of the logic state sequencer, and there are differences in the
code for
: the read section.  I haven't looked at it in detail.
:
: > I would think the "State Machine" ROM would be the
: > same. The data would be the same way per sector,
: > just 3 less sectors per track.
:
: There is more to it than just the number of sectors per track.
:
: There are differences in the way the disk bytes are encoded on
13-sector
: and 16-sector disks.  13-sector uses a "5-and-3" encoding
technique,
: while 16-sector uses "6-and-2".  (These terms refer to how data
bytes
: are split into bits to form disk bytes: "6-and-2" means that
each data
: byte of 8 bits is broken into a 6-bit disk byte and 2 bits
which are
: combined with 2 bits from each of two other data bytes to form
another
: disk byte.)
:
: The disk bytes are encoded using a table lookup technique
(Group Code
: Recording), which only allows some patterns of 1 and 0 bits to
be
: written to the disk (the restrictions are due to the
reliability of
: readback via the analog circuitry in the drive).
:
: From memory, the rules for 13-sector disks are:
:
: - Bit 7 must be set.  (This is a requirement of the Disk ][
controller
: for synchronization.)
: - No byte may contain two consecutive zero bits.
:
: If you work out all the possible combinations, this gives
slightly more
: than 32 valid disk bytes, which is sufficient to allow a 5-bit
encoding
: technique.
:
: For 16-sector disks, they relaxed the restrictions slightly:
:
: - No byte may contain more than one pair of consecutive zero
bits.
:
: This gives slightly more than 64 valid disk bytes, which is
enough to do
: a 6-bit encoding technique.
:
: Encoding one more data bit per disk byte allows fewer disk
bytes to be
: used to store an entire sector (about 341 disk bytes instead of
410), so
: the sectors occupy less space and more can be fit onto each
track.
: --
: David Empson
: dempson@actrix.gen.nz

Thank you David. I really must take some time
and read through all these books. After all,
I did buy them to learn from. What programs
can I use to convert a 13 sector disk image to
a real disk? From what you wrote above the 16
sector controller should be able to still write
one?

Bill @ GarberStreet Enterprizez };-)
Web Site - http://garberstreet.netfirms.com
Email - willy46pa @ comcast DOT net
Change DOT to a dot to contact me



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