PC87309VLJ datasheet(62/192 Pages) NSC

62 / 192 page

The Floppy Disk Controller (FDC) (Logical Device 0)

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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 “Bit 5 - DENSEL

Polarity Control” on page 30. (Default)

TABLE 3-13. DENSEL Encoding

Execution Phase

Internal registers are written.

Result Phase

None.

3.7.8

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

floppy disk controller (FDC) as a PC87309 by returning 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)

3.7.9

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.

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 3-14 on page 63.

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

µm, 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 FIG-

URE 3-5 on page 59. A gap 2 length of 41 bytes (at 1 or 2

Mbps) ensures that the preamble in the data field is com-

pletely 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 3-14 on page 63.

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 3-21 on page 72.

Bits 1,0 - Group Drive Mode Conﬁguration (GDC)

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)

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

76543210

00010010

DC3

DC2

DC1

DC0

GDC

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