Status
Register Identification
Pin
No. Name Function
Status Register
0
D7, IC
D7=0
and D6=0
D,
(Interrupt Normal termination of command,
Code) (NT).
Command was completed and properly
execulted.
D,=O and D,=I
Abnormal termination of command,
(AT).
Execution of command was started but
was not successfully completed.
D,=l and
D6=0
Invalid command issue, (IC).
Command which was issued was never
started.
D,=l and
D,=l
Abnormal termination because during
command execution the ready signal
from
FDD
changed state.
D,
SE When the FDC completes the Seek
(Seek End)
command, this flag is set to 1 (high).
D,
EC
If a fault signal is received from the
(Equipment
Check)
FDD,
or
if the track
0
signal falls to
occur after
77
step pulses (Recalibrate
Command) then this flag is set.
D,
NR When the FDD is in the not-ready
state and a Read or Write command is
issued, this flag is set. If a Read or
Write command is issued to side 1 of a
single-sided drive, then this flag is set.
(Not Ready)
D,
HD
(Head
This flag is used to indicate the state
of the head at interrupt.
Address)
D,
US, (Unit
This flag is used to indicate a drive
unit number at interrupt.
This flag is used to indicate a drive
unit number at interrupt.
Select
1)
Do
US,
(Unit
Select
0)
~ ~
Pin
No. Name Function
Status Register
1
D,
EN (End of
When the FDC tries to access a sector
beyond the final sector of a cylinder,
this flag is set.
Cylinder)
D6
D,
DE When the FDC detects a CRC(1)
Not used. This bit is always
0
(low).
error in either the
ID
field or the data
field, this flag is set.
(Data Error)
D, OR
If the FDC is not serviced by the host
system during data transfers within a
certain time interval, this flag
is
set.
(Overrun)
D,
Not used. This bit is always
0
(low).
D,
ND During execution of Read Data. Write
Deleted Data or Scan command, if the
FDC cannot find the sector specified
in the IDR(2) Register, this flag is set.
(No Data)
During execution of the Read ID
command, if the
FDC
cannot read the
ID
field without an error, then this
flag is set.
During execution of the Read A
Cylinder command, if the starting
sector cannot be found, then this flag
is set.
DI
NW (Not During execution of Write Data, Write
Writable) Deleted Data or Format A Cylinder
command, if the FDC detects a write
protect signal from the FDD, then this
flag is set.
Do MA (Missing If the FDC cannot detect the data
Address
Mark)
address mark or deleted data address
mark, this flag is set. Also at the same
time, the MD (missing address mark
in data field) of status register 2 is set.
F-23
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