PERPENDICULAR MODE
DATA BUS
PHASE
Command
R/W
W
D7
0
OW
D6 D5 D4 D3 D2
D1
1
GAP
D0
0
WGATE
REMARKS
Command Codes
0
0
0
1
0
0
D3 D2 D1 D0
INVALID CODES
DATA BUS
PHASE
R/W D7 D6 D5 D4 D3 D2 D1 D0
REMARKS
Command
W
───── Invalid Codes ─────
Invalid Command Codes
(NoOp - FDC goes into Stand-
by State)
Result
R
─────── ST0 ───────
ST0 = 80H
LOCK
DATA BUS
PHASE
Command
Result
R/W
W
R
D7
LOCK
0
D6 D5
D4
1
LOCK
D3 D2 D1 D0
REMARKS
Command Codes
0
0
0
0
0
0
1
0
0
0
0
0
SC is returned if the last command that was issued was the Format command. EOT is returned if the last
command was a Read or Write.
Note: These bits are used internally only. They are not reflected in the Drive Select pins. It is the user's
responsibility to maintain correspondence between these bits and the Drive Select pins (DOR).
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