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The controller waits the Delay Before Processing time

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

and then becomes idle. See “Idle Phase” on page 88.

Then, the controller issues pulses until the TRK0 disk

interface input signal becomes active or until the max-

imum number of RECALIBRATE step pulses have

been issued.

Table 54 shows the maximum number of RECALli-

BRATE step pulses that may be issued, depending on

the RECALIBRATE Step Pulses (R255) bit, bit 0 in

the second command phase byte of the MODE com-

mand (page 101), and the Extended Track Range

(ETR) bit, bit 4 of the third command byte of the

MODE command (page 101).

If the number of tracks on the disk drive exceeds the

maximum number of RECALIBRATE step pulses, it

may be necessary to issue another RECALIBRATE

command.

TABLE 54. Maximum RECALIBRATE Step Puls-

es for Values of R255 and ETR

The pulses actually occur while the controller is in the

drive polling phase. See “Drive Polling Phase” on

page 88.

An interrupt is generated after the TRK0 signal is as-

serted, or after the maximum number of RECALI-

BRATE step pulses is issued.

Software should ensure that the RECALIBRATE

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.

No command, except a SENSE INTERRUPT com-

mand, should be issued while a RECALIBRATE com-

mand is in progress.

Result Phase

None.

3.6.15 The RELATIVE SEEK Command

The RELATIVE SEEK command issues STEP pulses

that make the head of the selected drive step in or out

a programmable number of tracks.

Command Phase

First Command Phase Byte, Opcode,

Bit - 6 Step Direction DIR

This bit defines the step direction.

0 - Step head out.

1 - Step head in.

Second Command Phase Byte

See “Second Command Phase Byte” on page 96

for a description of the Drive Select (DS1,0) and

Head Select (HD) bits.

Third Command Phase Byte -

Relative Track Number (RTN)

This value specifies how many tracks the head

should step in or out from the current track.

Execution Phase

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.,

and then becomes idle. See “Idle Phase” on page 88.

Then, the controller enters the idle phase and issues

RTN STEP pulses until the TRK0 disk interface input

signal becomes active or until the specified number

(RTN) of STEP pulses have been issued. After the

RELATIVE SEEK operation is complete, the control-

ler generates an interrupt.

Software should ensure that the RELATIVE 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.

No command, except the SENSE INTERRUPT com-

mand, should be issued while a RELATIVE SEEK

command is in progress.

Result Phase

None.

R255

ETR

Maximum Number of

RECALIBRATE Step Pulses

85 (default)

255

3925

4095

7654

3210

DIR

1111

XXX

DS1

DS0

Relative Track Number (RTN)

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