PC87307VUL National Semiconductor, PC87307VUL Datasheet - Page 95

• Manufacturer Part Number: PC87307VUL
• Description: PC87307/PC97307 Plug and Play Compatible and PC97 Compliant SuperI/O
• Manufacturer: National Semiconductor

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.
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).
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 Figure
5-20. A gap 2 length of 41 bytes (at 1 or 2 Mbps) ensures
that the preamble 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.
OW
7
0
GDC Bits
1
0
0
1
1
250, 300 or 500 Kbps
TABLE 5-15. Effect of Drive Mode and Data Rate on FORMAT TRACK and WRITE DATA Commands
1 or 2 Mbps
Data Rates
6
0
0
0
1
0
1
0
DC3
TABLE 5-16. Effect of GDC Bits on FORMAT TRACK and WRITE DATA Commands
5
0
Perpendicular (1 or 2 Mbps)
Perpendicular ( 500 Kbps)
DC2
4
1
Conventional
Conventional
Drive Mode
DC1
Perpendicular
Perpendicular
Conventional
Conventional
3
0
Drive Mode
DC0
2
0
1
1
GDC
Length of Gap 2 in FORMAT
FORMAT TRACK Command
0
0
TRACK Command
Length of Gap 2 in
95
22 bytes
22 bytes
22 bytes
41 bytes
Bits 1,0 - Group Drive Mode Configuration (GDC)
Bits 5-2 -Drive 3-0 Mode Configuration (DC3-0)
Bit 7 - Overwrite (OW)
Execution Phase
Internal registers are written.
Result Phase
None.
22 bytes
22 bytes
22 bytes
41 bytes
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)
Portion of Gap 2 Rewritten in
Portion of Gap 2 Rewritten in
WRITE DATA Command
WRITE DATA Command
19 bytes
38 bytes
0 bytes
0 bytes
19 bytes
38 bytes
0 bytes
0 bytes
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