PC87309VLJ datasheet(70/192 Pages) NSC

70 / 192 page

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

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SCAN LOW OR EQUAL

SCAN HIGH OR EQUAL

First through Eighth Command Phase Bytes -

All Scan Commands

See READ DATA command for a description of the first

eight command phase bytes.

Ninth Command Phase Byte, Sector Step Size

During execution, the value of this byte is added to the cur-

rent sector number to determine the next sector to read.

Execution Phase

The most significant bytes of each sector are compared

first. If wildcard mode is enabled in bit 4 of the fourth com-

mand phase byte in the MODE command ( "Bit 4 - Scan

Wild Card (WLD)" on page 61), a value of FFh from either

the disk or the microprocessor always causes a match.

After each sector is read, if there is no match, the next sec-

tor is read. The next sector is the current sector number plus

the Sector Step Size specified in the ninth command phase

byte.

The scan operation continues until the condition is met, the

End of Track (EOT) is reached or the Terminal Count (TC)

signal becomes active.

Read error conditions during scan commands are the same

as read error conditions during the execution phase of the

READ DATA command. See Section 3.7.10 on page 64.

If the Skip Control (SK) bit is set to 1, sectors with deleted

data marks are ignored.

If all sectors read are skipped, the command terminates

with bit 3 of ST2 set to 1, i.e., disk data equals microproces-

sor data.

Result Phase

TABLE 3-20 shows how all the scan commands affect bits

3,2 of the Status 2 (ST2) result phase register. See Section

3.5.3 on page 49.

TABLE 3-20. The Effect of Scan Commands on the ST2

3.7.17

The SEEK Command

The SEEK command issues pulses of the STEP signal to

the selected drive, to move it in or out until the desired track

number is reached.

Software should ensure that the SEEK command is issued

for only one drive at a time. This is because the drives are

actually selected via the Digital Output Register (DOR),

which can only select one drive at a time. See Section 3.3.3

on page 39.

No command, except a SENSE INTERRUPT command,

should be issued while a SEEK command is in progress.

76543210

MFM

11001

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

Sector Step Size

76543210

MFM

11101

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

Sector Step Size

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

Command

Result Phase Status

Condition

Bit 3 - Scan

Satisﬁed

Bit 2 - Scan

Not Satisﬁed

SCAN

EQUAL

Disk =

µP

Disk

≠µP

SCAN LOW

OR EQUAL

Disk =

µP

Disk <

µP

Disk >

µP

SCAN HIGH

OR EQUAL

Disk =

µP

Disk >

µP

Disk <

µP

PC87309VLJ 数据表(PDF) 70 Page - National Semiconductor (TI)

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