PC87309VLJ datasheet(64/192 Pages) NSC

64 / 192 page

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

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3.7.10

The READ DATA Command

The READ DATA command reads logical sectors that con-

tain a normal data address mark from the selected drive and

makes the data available to the host microprocessor.

Command Phase

The READ DATA command phase bytes must specify the

following ID information for the desired sector:

Track number

Head number

Sector number

Bytes-per-sector code (See TABLE 3-10 on page 57.)

End of Track (EOT) sector number. This allows the con-

troller to read multiple sectors.

The value of the data length byte is ignored and must be

set to FFh.

After the last command phase byte is written, the controller

waits the Delay Before Processing time (see TABLE 3-24

on page 74) for the selected drive. During this time, the

drive motor must be turned on by enabling the appropriate

drive and motor select disk interface output signals via the

bits of the Digital Output Register (DOR). See Section 3.3.3

on page 39.

First Command Phase Byte

Bit 5 - Skip Control (SK)

This controls whether or not sectors containing a delet-

ed address mark will be skipped during execution of the

READ DATA command. See TABLE 3-16 on page 65.

0: Do not skip sector with deleted address mark.

1: Skip sector with deleted address mark.

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.

Bit 7 - Multi-Track (MT)

This bit controls whether or not the controller continues

to side 1 of the disk after reaching the last sector of side

0: Single track. The controller stops at the last sector

of side 0.

1: Multiple tracks. the controller continues to side 1 af-

ter reaching the last sector of side 0.

Second Command Phase Byte

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

These bits indicate which logical drive is active. See

“Bits 1,0 - Logical Drive Select (DS1,0)” on page 57.

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 (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.See “Bit 2 -

Head Select (HD)” on page 57.

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

lects side 0. (Default)

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

Bit 7 - Implied Seek (IPS)

This bit indicates whether or not an implied seek should

be performed. See also, “Bit 5 - Implied Seek (IPS)” on

page 60.

A software reset clears this bit to its default value of 0.

0: No implied seek operations. (Default)

1: The controller performs seek and sense interrupt

operations before executing the command.

Third Command Phase Byte - Track Number

The value in this byte specifies the number of the track

to read.

Fourth Command Phase Byte - Head Number

The value in this byte specifies head to use.

Fifth Command Phase Byte - Sector Number

The value in this byte specifies the sector to read.

Sixth 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 indicates the number of bytes that corre-

sponds to each code.

Seventh Command Phase Byte - End of Track (EOT) Sector

Number

This byte specifies the number of the sector at the End

Of the Track (EOT).

76543210

MFM

00110

IPS

XXXX

DS1

DS0

Track Number

Head Number

Sector Number

Bytes-Per-Sector Code

End of Track (EOT) Sector Number

Bytes Between Sectors - Gap 3

Data Length (Obsolete)

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