pc8477b National Semiconductor Corporation, pc8477b Datasheet - Page 25

• Manufacturer Part Number: pc8477b
• Description: Advanced Floppy Disk Controller
• Manufacturer: National Semiconductor Corporation

4 0 Command Set Description
Once the desired sector Address Field is found the control-
ler waits for the Data Separator to find the subsequent Data
Field for that sector If the Data Field (normal or deleted) is
not found with the expected time the controller terminates
the operation and enters the Result Phase (MD is set in
ST2) If a Deleted Data Mark is found and SK was set in the
Opcode command byte the controller skips this sector and
searches for the next sector Address Field as described
above The effect of SK on the Read Data command is
summarized in Table 4-6
Having found the Data Field the controller then transfers
data bytes from the disk drive to the host (described in Sec-
tion 5 3 Controller Phases) until the bytes per sector count
has been reached or the host terminates the operation
(through TC end of track or implicitly through overrun) The
controller will then generate the CRC for the sector and
compare this value with the CRC at the end of the Data
Field
Having finished reading the sector the controller will contin-
ue reading the next logical sector unless one or more of the
following termination conditions occurred
1 The DMA controller asserted TC The IC bits in ST0 are
2 The last sector address (of side 1 if MT was set) was
EOT
NC
S
e
set to Normal Termination
equal to EOT The EOT bit in ST1 is set The IC bits in
ST0 are set to Abnormal Termination This is the expect-
ed condition during Non-DMA transfers
0
0
0
0
1
1
1
1
MT
e
SK
SK
e
Sector Number last operated on by controller
0
0
1
1
0
0
1
1
No Change in Value
End of Track Sector Number from Command Phase
HD
0
0
1
1
0
0
1
1
Normal
Deleted
Normal
Deleted
Normal
Deleted
Normal
Deleted
Data Type
Data Type
TABLE 4-7 Result Phase Termination Values with No Error
Last Sector
TABLE 4-8 SK Effect on Read Deleted Data Command
k
e
k
e
k
e
k
e
EOT
EOT
EOT
EOT
EOT
EOT
EOT
EOT
TABLE 4-6 SK Effect on Read Data Command
Sector Read
Sector Read
N
N
(Continued)
Y
Y
Y
Y
Y
Y
Track
T
T
T
T
NC
NC
NC
NC
a
a
a
a
1
1
1
1
25
3 Overrun error The OR bit in ST1 is set The IC bits in ST0
4 CRC error The CE bit in ST1 and CD bit in ST2 are set
If MT was set in the Opcode command byte and the last
sector of side 0 has been transferred the controller will then
continue with side 1 starting with sector 1 and continuing
until EOT sector number is reached or TC occurs
Upon terminating the Execution Phase of the Read Data
command the controller will assert INT indicating the be-
ginning of the Result Phase The mP must then read the
result bytes from the FIFO The values that will be read back
in the result bytes are shown in Table 4-7 If an error occurs
the result bytes will indicate the sector read when the error
occurred
4 2 10 Read Deleted Data Command
The Read Deleted Data command reads logical sectors
containing a Deleted Data AM from the selected drive and
makes the data available to the host mP This command is
identical to the Read Data command except for the setting
of the CM bit in ST2 and the skipping of sectors The effect
of SK on the Read Deleted Data command is summarized in
Table 4-8 See Table 4-7 for the state of the result bytes for
a Normal Termination of the command
T
H
e
e
are set to Abnormal Termination If the mP cannot service
a transfer request in time the last correctly read byte will
be transferred
The IC bits in ST0 are set to Abnormal Termination
Track Number programmed in Command Phase
Head last selected by controller
CM Bit (ST2)
CM Bit (ST2)
ID Information at Result Phase
Head
NC
NC
NC
NC
H
H
0
0
0
1
0
1
1
0
1
0
Sector
S
S
S
S
a
a
a
a
1
1
1
1
1
1
1
1
Normal Termination
No Further Sectors Read
Normal Termination
Sector Skipped
No Further Sectors Read
Normal Termination
Sector Skipped
Normal Termination
Description of Results
Description of Results
Bytes Sector
NC
NC
NC
NC
NC
NC
NC
NC