PC87309VLJ datasheet(67/192 Pages) NSC

67 / 192 page

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

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TABLE 3-18. SK Effect on READ DELETED DATA

Command

Result Phase

3.7.12

The READ ID Command

The READ ID command finds the next available address

field and returns the ID bytes (track number, head number,

sector number, bytes-per-sector code) to the microproces-

sor in the result phase.

The controller reads the first ID Field header bytes it can

find and reports these bytes to the system in the result

bytes.

Command Phase

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, Opcode

See “Bit 6 - Modified Frequency Modulation (MFM)” on

page 57.

Second Command Phase Byte

See “Second Command Phase Byte” on page 57 for a

description of the Drive Select (DS1,0) and Head Select

(HD) bits.

Execution Phase

There is no data transfer during the execution phase of this

command. An interrupt is generated when the execution

phase is completed.

The READ ID command does not perform an implied seek.

After waiting the Delay Before Processing time, the control-

ler starts the data separator and waits for the data separator

to find the address field of the next sector. If an error condi-

tion occurs, the Interrupt Code (IC) bits in ST0 are set to ab-

normal termination (01), and the controller enters the result

phase.

Possible errors are:

The microprocessor aborted the command by writing to

the FIFO.

If there is no disk in the drive, the controller gets stuck.

The microprocessor must then write a byte to the FIFO

to advance the controller to the result phase.

Two pulses of the INDEX signal were detected since the

search began, and no Address Mark (AM) was found.

When the Address Mark (AM) is not found, the Missing

Address Mark bit (bit 0) is set in ST1. Section 3.5.2 on

page 49 describes the bits of ST1.

Result Phase

Skip

Control

(SK)

Data

Type

Sector

Read?

Control

Mark Bit 6

of ST2

Result

Normal

No More

Sectors Read

Deleted

Normal

Termination

Normal

Sector Skipped

Deleted

Normal

Termination

76543210

Result Phase Status Register 0 (ST0)

Result Phase Status Register 1 (ST1)

Result Phase Status Register 2 (ST2)

Track Number

Head Number

Sector Number

Bytes-Per-Sector Code

76543210

MFM

001010

XXXXX

DS1

DS0

76543210

Result Phase Status Register 0 (ST0)

Result Phase Status Register 1 (ST1)

Result Phase Status Register 2 (ST2)

Track Number

Head Number

Sector Number

Bytes-Per-Sector Code

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