Table 25 describes the effect of the SK bit on
the Read Deleted Data command execution and
results.
Read Deleted Data
This command is the same as the Read Data
command, only it operates on sectors that
contain a Deleted Data Address Mark at the
beginning of a Data Field.
Except where noted in Table 25, the C or R
value of the sector address is automatically
incremented (see Table 26).
Table 23 - Skip Bit vs. Read Deleted Data Command
DATA ADDRESS
RESULTS
SK BIT
VALUE
MARK TYPE
ENCOUNTERED
SECTOR CM BIT OF
DESCRIPTION
OF RESULTS
READ?
ST2 SET?
0
Normal Data
Yes
Yes
Address not
incremented.
Next sector not
searched for.
Normal
0
1
Deleted Data
Normal Data
Yes
No
No
termination.
Normal
Yes
termination.
Sector not read
("skipped").
Normal
1
Deleted Data
Yes
No
termination.
and sets the ND flag of Status Register 1
to a "1" if there is no comparison. Multi-track or
skip operations are not allowed with this
command. The MT and SK bits (bits D7 and D5
of the first command byte respectively) should
always be set to "0".
Read A Track
This command is similar to the Read Data
command except that the entire data field is
read continuously from each of the sectors of a
track. Immediately after encountering a pulse
on the nINDEX pin, the FDC starts to read
all data fields on the track as continuous blocks
of data without regard to logical sector numbers.
If the FDC finds an error in the ID or DATA CRC
check bytes, it continues to read data from the
track and sets the appropriate error bits at the
end of the command. The FDC compares the
ID information read from each sector with the
This command terminates when the EOT
specified number of sectors has not been read.
If the FDC does not find an ID Address Mark on
the diskette after the second occurrence of a
pulse on the IDX pin, then it sets the IC code in
Status Register
0
to "01" (abnormal
termination), sets the MA bit in Status Register
1 to "1", and terminates the command.
specified
value
in
the
command
59
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