PC87332VLJ datasheet(45/98 Pages) NSC

45 / 98 page

40 FDC Command Set Description (Continued)

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

SCAN EQUAL

Command Phase

MFM

IPS

DR1

DR0

Track Number

Drive Head Number

Sector Number

Bytes per Sector

End of Track Sector Number

Intersector Gap Length

Sector Step Size

Execution Phase

Data transferred from system to control-

ler is compared to data read from disk

Result Phase

MFM

IPS

DR1

DR0

Status Register 0

Status Register 1

Status Register 2

Track Number

Head Number

Sector Number

Bytes per Sector

SCAN HIGH OR EQUAL

Command Phase

MFM

IPS

DR1

DR0

Track Number

Drive Head Number

Sector Number

Bytes per Sector

End of Track Sector Number

Intersector Gap Length

Sector Step Size

Execution Phase

Data transferred from system to control-

ler is compared to data read from disk

Result Phase

Status Register 0

Status Register 1

Status Register 2

Track Number

Head Number

Sector Number

Bytes per Sector

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