PC87307 datasheet(94/218 Pages) NSC

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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

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

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)

Data Transfer

Rate (Kbps)

Multiplier

Head Settle

Time Range (msec)

250

0 - 120

300

6.666

0 - 100

500

0 - 60

1000

0 - 30

TABLE 5-14. DENSEL Encoding

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

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

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.

Bit 7

Bit 6

DENSEL Pin Deﬁnition

DENSEL low

DENSEL high

undeﬁned

Set by bit 5 of the SuperI/O FDC

conﬁguration register at offset F0h.

76543210

00011000

76543210

01110011

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