PC87309VLJ datasheet(57/192 Pages) NSC

57 / 192 page

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

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Command Phase

First Command Phase Byte, Opcode

Bit 6 - Modiﬁed Frequency Modulation (MFM)

This bit indicates the type of the disk drive and the data

transfer rate, and determines the format of the address

marks and the encoding scheme.

0: FM mode, i.e., single density.

1: MFM mode, i.e., double density.

TABLE 3-9. Typical Values for PC Compatible Diskette Media

1. Gap 2 is speciﬁed in the command phase of read, write, scan, and verify commands. Although this is the

recommended value, the FDC ignores this byte in read, write, scan and verify commands.

2. Gap 3 is the suggested value for the programmable GAP3 that is used in the FORMAT TRACK com-

mand and is illustrated in FIGURE 3-5 on page 59.

3. The 2.88 MB diskette media is a barium ferrite media intended for use in perpendicular recording drives

at the data rate of up to 1 Mbps.

Second Command Phase Byte

Bits 1,0 - Logical Drive Select (DS1,0)

These bits indicate which logical drive is active. They re-

flect the values of bits 1,0 of the Digital Output Register

(DOR) described in “Bits 1,0 - Drive Select” on page 40

and of result phase status registers 0 and 3 (ST0 and

ST3) described in Sections 3.5.1 on page 48 and 3.5.4

on page 50.

00: Drive 0 is selected. (Default)

01: Drive 1 is selected.

10: If four drives are supported, or drives 2 and 0 are

exchanged, drive 2 is selected.

11: If four drives are supported, drive 3 is selected.

Bit 2 - Head Select (HD)

This bit indicates which side of the Floppy Disk Drive

(FDD) is selected by the head. Its value is the inverse of

the HDSEL disk interface output signal.

This bit reflects the value of bit 3 of Status Register A

(SRA) described in Section 3.3.1 on page 38 and bit 2

of result phase status registers 0 and 3 (ST0 and ST3)

described in Sections 3.5.1 on page 48 and 3.5.4 on

page 50, respectively.

0: HDSEL is not active, i.e., the head of the FDD se-

lects side 0. (Default)

1: HDSEL is active, i.e., the head of the FDD selects

side 1.

Third Command Phase Byte -Bytes-Per-Sector Code

This byte contains a code in hexadecimal format that in-

dicates the number of bytes in a data field.

TABLE 3-10 on page 57 shows the number of bytes in

a data field for each code.

TABLE 3-10. Bytes per Sector Codes

Fourth Command Phase Byte - Sectors Per Track

The value in this byte specifies how many sectors there

are in the track.

Fifth Command Phase Byte - Bytes in Gap 3

The number of bytes in gap 3 is programmable. The

number to program for Gap 3 depends on the data

transfer rate and the type of the disk drive. TABLE 3-11

on page 58 shows some typical values to use for Gap 3.

76543210

MFM

001101

XXXXX

DS1

DS0

Bytes-Per-Sector Code

Sectors per Track

Bytes in Gap 3

Data Pattern

Media Type

Bytes in Data

Field (decimal)

Bytes-Per-Sector

Code (hex)

End of Track (EOT)

Sector # (hex)

Bytes in Gap 2 1

(hex)

Bytes in Gap 3 2

(hex)

360 KB

512

1.2 MB

512

720 KB

512

1.44 MB

512

2.88 MB3

512

Bytes-Per-Sector Code (hex)

Bytes in Data Field

128

256

512

1024

2048

4096

8192

16384

PC87309VLJ データシート(PDF) 57 Page - National Semiconductor (TI)

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