PC97338 datasheet(113/221 Pages) NSC

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Result Phase

Table 55 shows how all the scan commands affect

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

See “Result Phase Status Register 2 (ST2)” on page

90.

TABLE 55. The Effect of Scan Commands on the

ST2 Register

3.6.17 The SEEK Command

The SEEK command issues pulses of the STEP sig-

nal 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

time. See “Digital Output Register (DOR), Offset 010”

on page 77.

No command, except a SENSE INTERRUPT com-

mand, should be issued while a SEEK command is in

progress.

Command Phase

When bit 2 of the second command phase byte (ETR)

in the MODE command is set to 1, the track number

is stored as a 12-bit value. See “Bit 0 - Extended

Track Range (ETR)” on page 101.

In this case, a fourth command byte should be written

in the command phase to hold the Most Significant

Nibble (MSN), i.e., the four most significant bits, of the

number of the track to seek. Otherwise (ETR bit in

MODE is 0), this command phase byte is not required.

and, only three command bytes should be written.

After the last command byte is issued, the Drive Busy

bit for the selected drive is set in the Main Status Reg-

ister (MSR). See bits 3-0 in Section 3.3.6 on page 80.

The controller waits the Delay Before Processing time

(see Table 59 on page 117) for the selected drive, be-

fore issuing the first STEP pulse. After waiting the De-

lay Before Processing time, the controller becomes

idle. See “Idle Phase” on page 88.

Second Command Phase Byte

See READ DATA command for a description of

these bits.

Third Command Phase Byte,

Number of Track to Seek

The value in this byte is the number of the track to

seek.

7654

3210

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

7654

3210

0000

1111

XXX

DS1

DS0

Number of Track to Seek

MSN of Track # to Seek

0000

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