PC87338 datasheet(96/221 Pages) NSC

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3.6.4

The FORMAT TRACK Command

This command formats one track on the disk in IBM,

ISO, or Toshiba perpendicular format.

After a pulse from the INDEX signal is detected, data

patterns are written on the disk including all gaps, Ad-

dress Marks (AMs), address fields and data fields.

See Figure 58.

The format of the track is determined by the following

parameters:

• The MFM bit in the opcode (first command) byte,

which indicates the type of the disk drive and the

data transfer rate and determines the format of the

address marks and the encoding scheme.

• The Index Address Format (IAF) bit (bit 6 in the

second command phase byte) in the MODE com-

mand, which selects IBM or ISO format.

• The Group Drive Configuration (GDC) bits in the

PERPENDICULAR MODE command, which se-

lect either conventional or Toshiba perpendicular

format.

• A bytes-per-sector code, which determines the

sector size. See Table 44 on page 97.

• A sectors per track parameter, which specifies

how many sectors are formatted on the track.

• The data pattern byte, which is used to fill the data

field of each sector.

Table 45 shows typical values for these parameters

for specific PC compatible diskettes.

To allow flexible formatting, the microprocessor must

supply the four address field bytes (track number,

head number, sector number, bytes-per-sector code)

for each sector formatted during the execution phase.

This allows non-sequential sector interleaving.

This transfer of bytes from the microprocessor to the

controller can be done in DMA or non-DMA mode

(See Section 3.4.2 on page 85), with the FIFO en-

abled or disabled.

The FORMAT TRACK command terminates when a

pulse from the INDEX signal is detected a second

time, at which point an interrupt is generated.

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.

Second Command Phase Byte

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

These bits indicate which logical drive is active.

They reflect the values of bits 1,0 of the Digital

Output Register (DOR) described on page 88 and

of result phase status registers 0 and 3 (ST0 and

ST3) described on pages 88 and 91, respectively.

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 select-

ed.

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 sig-

nal.

This bit reflects the value of bit 3 of Status Register

A (SRA) described on page 76 and bit 2 of result

phase status registers 0 and 3 (ST0 and ST3) de-

scribed on pages 88 and 91, respectively.

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

selects side 0. (Default)

1 - HDSEL is active, i.e., the head of the FDD se-

lects side 1.

Third Command Phase Byte -

Bytes-Per-Sector Code

This byte contains a code in hexadecimal format

that indicates the number of bytes in a data field.

7654

3210

MFM

1101

XXX

DS1

DS0

Bytes-Per-Sector Code

Sectors per Track

Bytes in Gap 3

Data Pattern

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