DP8473N NSC [National Semiconductor], DP8473N Datasheet - Page 16

• Manufacturer Part Number: DP8473N
• Description: DP8473 Floppy Disk Controller PLUS-2
• Manufacturer: NSC [National Semiconductor]

Command Description
READ DATA
The Read Data op-code is written to the data register fol-
lowed by 8 bytes as specified in the Command Description
Table After the last byte is written the controller starts
looking for the correct sector header Once the sector is
found the controller sends the data to the
sector is finished the Sector Number is incremented by one
and this new sector is searched for If MT (Multi-Track) is
set both sides of one track can be read Starting on side
zero the sectors are read until the sector number specified
by End of Track Sector Number is reached Then side one
is read starting with sector number one
In DMA mode the Read Data command continues to read
until the TC pin is set This means that the DMA controller
should be programmed to transfer the correct number of
bytes TC could be controlled by the
when enough bytes are received An alternative to these
methods of stopping the Read Data command is to program
the End of Track Sector Number to be the last sector num-
ber that needs to be read The controller will stop reading
the disk with an error indicating that it tried to access a
sector number beyond the end of the track
The Number of Data Bytes per Sector parameter is defined
in Table IX If this is set to zero then the Data Length param-
eter determines the number of bytes that the controller
transfers to the
than 128 the controller still reads the entire 128 byte sector
and checks the CRC though only the number of bytes spec-
ified by the Data Length parameter are transferred to the
Bytes per Sector parameter is not zero the Data Length
parameter has no meaning and should be set to FF (hex)
If the Implied Seek Mode is enabled by both the Mode com-
mand and the IPS bit in this command a Seek will be per-
formed to the track number specified in the Command
Phase The controller will also wait the Head Settle time if
the implied seek is enabled
After all these conditions are met the controller searches
for the specified sector by comparing the track number
head number sector number and number bytes sector giv-
en in the Command Phase with the appropriate bytes read
off the disk in the Address Fields
If the correct sector is found but there is a CRC error in the
Address Field bit 5 of ST1 (CRC Error) is set and an abnor-
mal termination is indicated If the correct sector is not
P Data Length should not be set to zero If the Number of
P If the data length specified is smaller
EOT
NC
S
T
e
e
MT
e
0
0
0
0
1
1
1
1
Track Number programmed in Command Phase
e
Sector Number last operated on by controller
No Change in Value
End of Track Sector Number from Command Phase
TABLE X Result Phase Termination Values with No Error
HD
0
0
1
1
0
0
1
1
P and be asserted
Sector
k
e
k
e
k
e
k
e
Last
P After one
EOT
EOT
EOT
EOT
EOT
EOT
EOT
EOT
Track
T
T
T
NC
NC
NC
NC
NC
a
a
a
16
1
1
1
ID Information at Result Phase
found bit 2 of ST1 (No Data) is set and an abnormal termi-
nation is indicated In addition to this if any Address Field
track number is FF bit 1 of ST2 (Bad Track) is set or if any
Address Field track number is different from that specified in
the Command Phase bit 4 of ST2 (Wrong Track) is set
After finding the correct sector the controller reads that
Data Field If a Deleted Data Mark is found and the SK bit is
set the sector is not read bit 6 of ST2 (Control Mark) is set
and the next sector is searched for If a deleted data mark is
found and the SK bit is not set the sector is read bit 6 of
ST2 (Control Mark) is set and the read terminates with a
normal termination If a CRC error is detected in the Data
Field bit 5 is set in both ST1 and ST2 (CRC Error) and an
abnormal termination is indicated
If no problems occur in the read command the read will
continue from one sector to the next in logical order (not
physical order) until either TC is set or an error occurs
If a disk has not been inserted into the disk drive there are
many opportunities for the controller to appear to hang up It
does this if it is waiting for a certain number of disk revolu-
tions for something If this occurs the controller can be
forced to abort the command by writing a byte to the Data
register This will place the controller into the Result Phase
An interrupt will be generated when the Execution Phase of
the Read Data command terminates The values that will be
read back in the Result Phase are shown in Table X If an
error occurs the result bytes will indicate the sector being
read when the error occurred
READ DELETED DATA
This command is the same as the Read Data command
except for its treatment of a Deleted Data Mark If a Deleted
Head
NC
NC
NC
NC
NC
NC
1
0
TABLE IX Sector Size Selection
Bytes Sector
Sector
S
S
S
S
a
a
a
a
1
1
1
1
Code
1
1
1
1
0
1
2
3
4
5
6
B S
NC
NC
NC
NC
NC
NC
NC
NC
of Bytes in
Data Field
Number
1024
2048
4096
8192
128
256
512