PC87307 Datasheet, PDF (94/218 Pages) National Semiconductor (TI) – PC87307/PC97307 Plug and Play Compatible and PC97 Compliant SuperI/O

Fourth Command Phase Byte
Bits 3-0 - Head Settle Factor
This field is used to specify the maximum time allowed
for the read/write head to settle after a seek during an
implied seek operation.
The value specified by these bits (the head settle factor)
is multiplied by the multiplier for selected data rate to
specify a head settle time that is within the range for that
data rate.
Use the following formula to determine the head settle
factor that these bits should specify:
Head Settle Factor x Multiplier = Head Settle Time
Table 5-13 shows the multipliers and head settle time
ranges for each data transfer rate. The default head set-
tle factor, i.e., value for these bits, is 8.
TABLE 5-13. Multipliers and Head Settle Time Ranges
for Different Data Transfer Rates
Data Transfer
Rate (Kbps)
250
300
500
1000
Multiplier
8
6.666
4
2
Head Settle
Time Range (msec)
0 - 120
0 - 100
0 - 60
0 - 30
TABLE 5-14. DENSEL Encoding
Bit 7
0
0
1
1
Bit 6
0
1
0
1
DENSEL Pin Definition
DENSEL low
DENSEL high
undefined
Set by bit 5 of the SuperI/O FDC
configuration register at offset F0h.
Execution Phase
Internal registers are written.
Result Phase
None.
5.7.8 The NSC Command
The NSC command can be used to distinguish between the
FDC versions and the 82077.
Command Phase
7
6
5
4
3
2
1
0
0
0
0
1
1
0
0
0
Bit 4 - Scan Wild Card (WLD)
This bit determines whether or not a value of FFh from
either the microprocessor or the disk is recognized dur-
ing a scan command as a wildcard character.
0 - A value of FFh from either the microprocessor or
the disk during a scan command is interpreted as a
wildcard character that always matches. (Default)
1 - The scan commands do not recognize a value of
FFh as a wildcard character.
Bit 5 - CMOS Disk Interface Buffer Enable (BFR)
This bit configures drive output signals.
0 - Drive output signals are configured as standard 4
mA push-pull output signals (40 mA sink, 4 mA
source). (Default)
1 - Drive output signals are configured as 40 mA open-
drain output signals.
Bits 7,6 - Density Select Pin Configuration (DENSEL)
This field can configure the polarity of the Density Select
output signal (DENSEL) as always low or always high,
as shown in Table 4-3. This allows the user more flexi-
bility with new drive types.
This field overrides the DENSEL polarity defined by the
DENSEL polarity bit of the SuperI/O FDC configuration
register at index F0h and described on page 36.
00 - The DENSEL signal is always low.
01 - The DENSEL signal is always high.
10 - The DENSEL signal is undefined.
11 - The polarity of the DENSEL signal is defined by
the DENSEL Polarity bit (bit 5) of the SuperI/O
FDC configuration register. See page 37. (Default)
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)
.
7
6
5
4
3
2
1
0
0
1
1
1
0
0
1
1
5.7.9 The PERPENDICULAR MODE Command
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.
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