DP8473N NSC [National Semiconductor], DP8473N Datasheet - Page 17

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

Command Description
Data Mark is read the sector is read normally If a Regular
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 Regular 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
WRITE DATA
The Write Data command is very similar to the Read Data
command except that data is transferred from the P to the
disk rather than the other way around If the controller de-
tects the Write Protect signal bit 1 of ST1 (Not Writable) is
set and an abnormal termination is indicated
WRITE DELETED DATA
This command is the same as the Write Data Command
except a Deleted Data Mark is written at the beginning of
the Data Field instead of the normal Data Mark
READ A TRACK
This command is similar to the Read Data command except
for the following The controller starts at the index hole and
reads the sectors in their physical order not their logical
order
Even though the controller is reading sectors in their physi-
cal order it will still perform a comparison of the header ID
bytes with the Data programmed in the Command Phase
The exception to this is the sector number Internally this is
initialized to a one and then incremented for each succes-
sive sector read Whether or not the programmed Address
Field matches that read from the disk the sectors are still
read in their physical order If a header ID comparison fails
bit 2 of ST1 (No Data) is set but the operation will continue
If there is a CRC error in the Address Field or the Data Field
the read will also continue
The command will terminate when it has read the number of
sectors programmed in the EOT parameter
READ ID
This command will cause the controller to read the first Ad-
dress Field that it finds The Result Phase will contain the
header bytes that are read There is no data transfer during
the Execution Phase of this command An interrupt will be
generated when the Execution Phase is completed
FORMAT A TRACK
This command will format one track on the disk After the
index hole is detected data patterns are written on the disk
including all gaps address marks Address Fields and Data
Fields The exact details of the number of bytes for each
field is controlled by the parameters given in the Format A
Track command and the IAF (Index Address Field) bit in the
Mode command The Data Field consists of the Fill Byte
specified in the command repeated to fill the entire sector
To allow for flexible formatting the P must supply the four
Address Field bytes (track head sector number of bytes)
(Continued)
17
for each sector formatted during the Execution Phase In
other words as the controller formats each sector it will
request four bytes through either DMA requests or inter-
rupts This allows for non-sequential sector interleaving
Some typical values for the programmable GAP size are
shown in Table XI
The Format Command terminates when the index hole is
detected a second time at which point an interrupt is gener-
ated Only the first three status bytes in the Result Phase
are significant
Note Format Gap is the gap length used only for the Format command
125 kb s
250 kb s
250 kb s
500 kb s
Media
360k
1 2M
720k
1 44M
Type
Mode
MFM
MFM
FM
FM
Format Table for PC Compatible Diskette Media
TABLE XI Gap Length for Various Sector Sizes
Format Table for Sector Size and Data Rate
decimal
Sector
Size
decimal
512
512
512
512
Sector
1024
2048
1024
2048
4096
1024
2048
4096
1024
2048
4096
8192
Size
128
128
256
512
256
256
512
512
128
256
512
256
512
512
and Disk Types
Sector
Code
Sector
hex
Code
02
02
02
02
hex
00
00
01
02
03
04
01
01
02
02
03
04
05
00
01
02
03
04
05
01
02
02
03
04
05
06
EOT
hex
EOT
09
0F
09
12
hex
12
10
08
04
02
01
12
10
08
09
04
02
01
1A
0F
08
04
02
01
1A
0F
12
08
04
02
01
Sector
Sector
Gap
hex
Gap
2A
1B
1B
1B
hex
C8
C8
0A
2A
1B
C8
C8
0E
1B
C8
C8
0E
1B
1B
C8
C8
07
10
18
46
20
80
07
47
35
99
Format
Format
Gap
Gap
hex
hex
6C
50
54
50
FF
FF
0C
F0
FF
FF
1B
2A
3A
8A
FF
FF
6C
FF
FF
FF
09
19
30
87
32
50
50
36
54
74