PC87306 datasheet(44/110 Pages) NSC

44 / 110 page

40 FDC Command Set Description (Continued)

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

4115 Scan Commands

The Scan commands allow data read from the disk to be

compared against data sent from the mP using ones com-

plement arithmetic sector by sector

There are three Scan commands to choose from

1 Scan Equal checks to see if the scanned value of the

disk data is equal to that of the mP data The scan con-

dition is therefore disk data e mP data

2 Scan Low or Equal checks to see if the scanned val-

ue of the disk data is equal to or less than that of the mP

data The scan condition is therefore disk data s data

3 Scan High or Equal checks to see if the scanned val-

ue of the disk data is equal to or greater than that of the

P data The scan condition is therefore disk data t

P data

The results of these comparisons are indicated in the Status

the three commands follows

Each sector is compared starting with the most significant

bytes first and where the next sector is defined as the cur-

rent Sector Number plus the Sector Step Size Reading of

sectors continues until either the scan condition is met the

End of Track (EOT) has been reached or the Terminal

Count (TC) is asserted

If the Wildcard mode is enabled in the Mode command an

FFh from either the disk or the mP is used as a don’t care

byte that will always match equal Read errors on the disk

will have the same error conditions as the Read Data com-

mand

Additionally if the Skip Flag (SK) bit is set sectors with

deleted data marks will be ignored If all sectors read are

skipped the command will terminate with bit 3 of the Status

TABLE 4-13 Scan Command Termination Values

Command

Comparison

Condition

Status

Condition

Met

Indicated

Result

Scan Equal Disk Data e

Yes

Disk Data e

P Data

Disk Data i

P Data

Scan Low

Disk Data s

Yes

Disk Data e

or Equal

P Data

Yes

Disk Data k

P Data

Disk Data l

P Data

Scan High

Disk Data t

Yes

Disk Data e

or Equal

P Data

Yes

Disk Data l

P Data

Disk Data k

P Data

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