pc87317vul National Semiconductor Corporation, pc87317vul Datasheet - Page 121

• Manufacturer Part Number: pc87317vul
• Description: Pc87317vul/pc97317vul Superi/o Plug And Play Compatible With Acpi Compliant Controller/extender
• Manufacturer: National Semiconductor Corporation

Execution Phase
Internal registers are written.
Result Phase
None.
5.7.8
The NSC command can be used to distinguish between the
FDC versions and the 82077.
Command Phase
Execution Phase
Result Phase.
The result phase byte of the NSC command identifies the
module as the floppy disk controller (FDC) of NSC by re-
turning a value of 73h.
The 82077 and DP8473 return the value 80h, signifying an
invalid command.
Bits 3-0 of this result byte are subject to change by NSC,
and specify the version of the Floppy Disk Controller (FDC)
5.7.9
The PERPENDICULAR MODE command configures each
of the four logical disk drives for perpendicular or conven-
tional mode via the logical drive configuration bits 1,0 or 5-
2, depending on the value of bit 7. The default mode is con-
ventional. Therefore, if the drives in the system are conven-
tional, it is not necessary to issue a PERPENDICULAR
MODE command.
This command supports the unique FORMAT TRACK and
WRITE DATA requirements of perpendicular (vertical) re-
cording disk drives with a 4 MB unformatted capacity.
Perpendicular recording drives operate in extra high density
mode at 1 or 2 Mbps, and are downward compatible with
1.44 MB and 720 KB drives at 500 kbps (high density) and
250 kbps (double density), respectively.
If the system includes perpendicular drives, this command
should be issued during initialization of the FDC. Then,
when a drive is accessed for a FORMAT TRACK or WRITE
DATA command, the FDC adjusts the command parame-
ters based on the data rate. See TABLE 5-15 "Effect of
Drive Mode and Data Rate on FORMAT TRACK and
WRITE DATA Commands" on page 122.
Precompensation is set to zero for perpendicular drives at
any data rate.
Perpendicular recording type disk drives have a pre-erase
head that leads the read or write head by 200 m, which
translates to 38 bytes at a 1 Mbps data transfer rate (19
bytes at 500 Kbps).
7
0
7
0
The NSC Command
The PERPENDICULAR MODE Command
6
0
6
1
5
0
5
1
4
1
4
1
3
1
3
0
2
0
2
0
1
0
1
1
0
0
0
1
121
The increased space between the two heads requires a
larger gap 2 between the address field and data field of a
sector at 1 or 2 Mbps. See Perpendicular Format in FIG-
URE 5-19 "IBM, Perpendicular, and ISO Formats Support-
ed by the FORMAT TRACK Command" on page 118. A gap
2 length of 41 bytes (at 1 or 2 Mbps) ensures that the pre-
amble in the data field is completely pre-erased by the pre-
erase head.
Also, during WRITE DATA operations to a perpendicular
drive, a portion of gap 2 must be rewritten by the controller
to guarantee that the data field preamble has been pre-
erased. See TABLE 5-15.
Command Phase
Second Command Phase Byte
A hardware reset clears all the bits to zero (conventional
mode for all drives). PERPENDICULAR MODE command
bits may be written at any time.
The settings of bits 1 and 0 in this byte override the logical
drive configuration set by bits 5 through 2. If bits 1 and 0 are
both 0, bits 5 through 2 configure the logical disk drives as
conventional or perpendicular. Otherwise, bits 2 and 0 con-
figure them. See TABLE 5-16 "Effect of GDC Bits on FOR-
MAT TRACK and WRITE DATA Commands" on page 122.
Bits 1,0 - Group Drive Mode Configuration (GDC)
Bits 5-2 -Drive 3-0 Mode Configuration (DC3-0)
Bit 7 - Overwrite (OW)
OW
7
0
These bits configure all the logical disk drives as con-
ventional or perpendicular. If the Overwrite bit (OW, bit
7) is 0, this setting may be overridden by bits 5-2.
It is not necessary to issue the FORMAT TRACK com-
mand if all drives are conventional.
These bits are cleared to 0 by a software reset.
00: Conventional. (Default)
01: Perpendicular. (500 Kbps)
10: Conventional.
11: Perpendicular. (1 or 2 Mbps)
If bits 1,0 are both 0, and bit 7 is 1, these bits configure
logical drives 3-0 as conventional or perpendicular. Bits
5-2 (DC3–0) correspond to logical drives 3-0, respec-
tively.
These bits are not affected by a software reset.
0: Conventional drive. (Default)
1: Perpendicular drive.
This bit enables or disables changes in the mode of the
logical drives by bits 5-2.
0: Changes in mode of logical drives via bits 5-2 are
1: Changes enabled.
It is not necessary to issue the FORMAT TRACK
command for conventional drives.
ignored. (Default)
6
0
0
DC3
5
0
DC2
4
1
DC1
3
0
DC0
2
0
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1
1
GDC
0
0