STATUS REGISTER ENCODING
During the Result Phase of certain commands, the Data Register contains data bytes that give the status of the
command just executed.
Table 12 - Status Register 0
BIT NO.
SYMBOL
IC
NAME
DESCRIPTION
7,6
Interrupt Code 00 - Normal termination of command. The specified
command was properly executed and completed without
error.
01 - Abnormal termination of command. Command
execution was started, but was not successfully
completed.
10 - Invalid command. The requested command could
not be executed.
11 - Abnormal termination caused by Polling.
5
4
SE
EC
Seek End
The FDC completed a Seek, Relative Seek or
Recalibrate command (used during a Sense Interrupt
Command).
The TRK0 pin failed to become a "1" after:
1. 80 step pulses in the Recalibrate command.
2. The Relative Seek command caused the FDC to
step outward beyond Track 0.
Equipment
Check
3
2
1,0
Unused. This bit is always "0".
Head Address The current head address.
Drive Select The current selected drive.
H
DS1,0
Table 13 - Status Register 1
NAME
End of
BIT NO.
SYMBOL
EN
DESCRIPTION
7
The FDC tried to access a sector beyond the final sector
of the track (255D). Will be set if TC is not issued after
Read or Write Data command.
Cylinder
6
5
Unused. This bit is always "0".
The FDC detected a CRC error in either the ID field or
the data field of a sector.
Becomes set if the FDC does not receive CPU or DMA
service within the required time interval, resulting in data
overrun or underrun.
DE
OR
Data Error
4
Overrun/
Underrun
3
2
Unused. This bit is always "0".
Any one of the following:
ND
No Data
1. Read Data, Read Deleted Data command - the FDC
did not find the specified sector.
2. Read ID command - the FDC cannot read the ID field
without an error.
3. Read A Track command - the FDC cannot find the
proper sector sequence.
1
0
NW
MA
Not Writeable WP pin became a "1" while the FDC is executing a Write
Data, Write Deleted Data, or Format A Track command.
Missing
Any one of the following:
Address Mark 1. The FDC did not detect an ID address mark at the
specified track after encountering the index pulse
from the nINDEX pin twice.
2. The FDC cannot detect a data address mark or a
deleted data address mark on the specified track.
Page 32
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