(Source: Beneath Apple ProDOS, Appendix D. Additional notes by Christer Ericson, christer@cs.umu.se)
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CODE OPERATION BEFORE AFTER
0 CLR XXXXXXXX 00000000
8 NOP ABCDEFGH ABCDEFGH
9 SL0 ABCDEFGH BCDEFGH0
A SR (write protected) ABCDEFGH 11111111
(not write protected) ABCDEFGH 0ABCDEFG
B LOAD XXXXXXXX YYYYYYYY
D SL1 ABCDEFGH BCDEFGH1
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ADDRESS Q6 Q7
$C08C OFF ---
$C08D ON ---
$C08E --- OFF
$C08F --- ON
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Q6 ON, Q7 OFF (Check write protect)
HIGH BIT CLEAR HIGH BIT SET
STATE PULSE NO PULSE PULSE NO PULSE
0 0A 0A 0A 0A
1 0A 0A 0A 0A
2 0A 0A 0A 0A
3 0A 0A 0A 0A
4 0A 0A 0A 0A
5 0A 0A 0A 0A
6 0A 0A 0A 0A
7 0A 0A 0A 0A
8 0A 0A 0A 0A
9 0A 0A 0A 0A
A 0A 0A 0A 0A
B 0A 0A 0A 0A
C 0A 0A 0A 0A
D 0A 0A 0A 0A
E 0A 0A 0A 0A
F 0A 0A 0A 0A
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Q6 OFF, Q7 OFF (Read)
HIGH BIT CLEAR HIGH BIT SET
STATE PULSE NO PULSE PULSE NO PULSE
0 18 18 18 18
1 2D 2D 38 38
2 D8 38 08 28*
3 D8 48 48 48
4 D8 58 D8 58
5 D8 68 D8 68
6 D8 78 D8 78
7 D8 88 D8 88
8 D8 98 D8 98
9 D8 29 D8 A8
A CD BD D8 B8
B D9 59 D8 C8
C D9 D9 D8 A0
D D8** 08 E8 E8
E FD FD F8 F8
F DD 4D E0 E0
*) Here is where the state machine loops, discarding sync bits
when the high bit of the shift register is set.
**) Here is where the state machine hangs in that copy protection
scheme that is based on a special disk of which portions of a
track is written such that one bits arrive for each and every
state of the state machine. (This protection reveals itself
in that Copy II Plus and other bit copiers think the track
is much much longer than the normal $1880, or so, nibbles.)
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Q7 ON (Write)
Q6 OFF Q6 ON
HIGH BIT HIGH BIT
STATE CLEAR SET CLEAR SET
0 18 18 18 18
1 28 28 28 28
2 39 39 3B 3B
3 48 48 48 48
4 58 58 58 58
5 68 68 68 68
6 78 78 78 78
7 08 88 08 88
8 98 98 98 98
9 A8 A8 A8 A8
A B9 B9 BB BB
B C8 C8 C8 C8
C D8 D8 D8 D8
D E8 E8 E8 E8
E F8 F8 F8 F8
F 88 08 88 08