PC87332 datasheet(44/98 Pages) NSC

44 / 98 page

40 FDC Command Set Description (Continued)

3 If the Address Field ID comparison fails the controller

sets ND in ST1 but continues to read the sector If there

is a CRC error in the Address Field the controller sets CE

in ST1 but continues to read the sector

4 Multi-track and Skip operations are not allowed SK and

MT should be set to 0

5 If there is a CRC error in the Data Field the controller

sets CE in ST1 and CD in ST2 but continues reading

sectors

6 The controller reads a maximum of EOT physical sectors

There is no support for multi-track reads

Command Phase

MFM

IPS

DR1

DR0

Track Number

Drive Head Number

Sector Number

Bytes per Sector

End of Track Sector Number

Intersector Gap Length

Data Length

Execution Phase

Data read from disk drive is transferred

to system via DMA or non-DMA modes

Result Phase

Status Register 0

Status Register 1

Status Register 2

Track Number

Head Number

Sector Number

Bytes per Sector

4113 Recalibrate Command

The Recalibrate command is very similar to the Seek com-

mand The controller sets the Present Track Register (PTR)

of the selected drive to zero It then steps the head of the

selected drive out until the TRK0 disk interface input signal

goes active or until the maximum number of step pulses

have been issued See Table 4-12 for the maximum recali-

brate step pulse values based on the R255 and ETR bits in

the Mode command If the number of tracks on the disk

drive exceeds the maximum number of recalibrate step

pulses another Recalibrate command may need to be is-

sued

TABLE 4-12 Maximum Recalibrate

Step Pulses Based on R255 and ETR

R255

ETR

Maximum Recalibrate

Step Pulses

85 (default)

255

3925

4095

After the last command byte is issued the DRx BUSY bit is

set in the MSR for the selected drive The controller will

simulate the Motor On time and then enter the Idle Phase

The execution of the actual step pulses occur while the con-

troller is in the Drive Polling Phase An interrupt will be gen-

erated after the TRK0 signal is asserted or after the maxi-

mum number of recalibrate step pulses are issued There is

no Result Phase Recalibrates should not be issued on

more than one drive at a time This is because the drives are

actually selected via the DOR which can only select one

drive at a time No other command except the Sense Inter-

rupt command should be issued while a Recalibrate com-

mand is in progress

Command Phase

000001

000000DR1

DR0

Execution Phase

Disk drive head is stepped out to Track 0

Result Phase

None

4114 Relative Seek Command

The Relative Seek command steps the selected drive in or

out a given number of steps This command will step the

readwrite head an incremental number of tracks as op-

posed to comparing against the internal present track regis-

ter for that drive

Command Phase

DIR

DR1

DR0

Execution Phase

Disk drive head stepped in or out a pro-

grammable number of tracks

Result Phase

None

The Relative Seek parameters are defined as follows

DIR

ReadWrite Head Step Direction Control

0 e

Step Head Out

1 e

Step Head In

RTN

Relative Track Number This value will determine how

many incremental tracks to step the head in or out

from the current track number

The controller will issue RTN number of step pulses and

update the Present Track Register for the selected drive

The one exception to this is if the TRK0 disk input goes

active which indicates that the drive readwrite head is at

the outermost track In this case the step pulses for the

Relative Seek are terminated and the PTR value is set ac-

cording to the actual number of step pulses issued The

arithmetic is done modulo 255 The DRx BUSY bit in the

MSR is set for the selected drive The controller will simu-

late the Motor On time before issuing the step pulses After

the Motor On time the controller will enter the Idle Phase

The execution of the actual step pulses occurs in the Idle

Phase of the controller

After the step operation is complete the controller will gen-

erate an interrupt There is no Result Phase Relative Seeks

should not be issued on more than one drive at a time This

is because the drives are actually selected via the DOR

which can only select one drive at a time No other com-

mand except the Sense Interrupt command should be is-

sued while a Relative Seek command is in progress

PC87332 Datasheet(PDF) 44 Page - National Semiconductor (TI)

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