Write Deleted Data
This command is almost the same as the Write Data command except that a Deleted Data Address Mark is written at
the beginning of the Data Field instead of the normal Data Address Mark. This command is typically used to mark a
bad sector containing an error on the floppy disk.
Verify
The Verify command is used to verify the data stored on a disk. This command acts exactly like a Read Data
command except that no data is transferred to the host. Data is read from the disk and CRC is computed and
checked against the previously-stored value.
Because data is not transferred to the host, TC (pin 25) cannot be used to terminate this command. By setting the
EC bit to “1”, an implicit TC will be issued to the FDC. This implicit TC will occur when the SC value has
decremented to 0 (an SC value of 0 will verify 256 sectors). This command can also be terminated by setting the EC
bit to “0” and the EOT value equal to the final sector to be checked. If EC is set to “0”, DTL/SC should be
programmed to 0FFH. Refer to Table 41 and Table 42 for information concerning the values of MT and EC versus
SC and EOT value.
Definitions:
# Sectors Per Side = Number of formatted sectors per each side of the disk.
# Sectors Remaining = Number of formatted sectors left which can be read, including side 1 of the disk if MT is set to
“1”.
Table 42 - Verify Command Result Phase Table
MT
EC
SC/EOT VALUE
TERMINATION RESULT
0
0
SC = DTL
Success Termination
EOT £ # Sectors Per Side
Result Phase Valid
0
0
0
1
1
1
1
0
1
1
0
0
1
1
SC = DTL
EOT > # Sectors Per Side
Unsuccessful Termination
Result Phase Invalid
SC £ # Sectors Remaining AND
EOT £ # Sectors Per Side
Successful Termination
Result Phase Valid
SC > # Sectors Remaining OR
EOT > # Sectors Per Side
Unsuccessful Termination
Result Phase Invalid
SC = DTL
EOT £ # Sectors Per Side
Successful Termination
Result Phase Valid
SC = DTL
EOT > # Sectors Per Side
Unsuccessful Termination
Result Phase Invalid
SC £ # Sectors Remaining AND
EOT £ # Sectors Per Side
Successful Termination
Result Phase Valid
SC > # Sectors Remaining OR
EOT > # Sectors Per Side
Unsuccessful Termination
Result Phase Invalid
Note: If MT is set to “1” and the SC value is greater than the number of remaining formatted sectors on Side 0,
verifying will continue on Side 1 of the disk.
Format A Track
The Format command allows an entire track to be formatted. After a pulse from the IDX pin is detected, the FDC
starts writing data on the disk including gaps, address marks, ID fields, and data fields per the IBM System 34 or 3740
format (MFM or FM respectively). The particular values that will be written to the gap and data field are controlled by
the values programmed into N, SC, GPL, and D which are specified by the host during the command phase. The
data field of the sector is filled with the data byte specified by D. The ID field for each sector is supplied by the host;
that is, four data bytes per sector are needed by the FDC for C, H, R, and N (cylinder, head, sector number and
sector size respectively).
After formatting each sector, the host must send new values for C, H, R and N to the FDC for the next sector on the
track. The R value (sector number) is the only value that must be changed by the host after each sector is formatted.
This allows the disk to be formatted with nonsequential sector addresses (interleaving). This incrementing and
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