PC87332VLJ-5 NSC [National Semiconductor], PC87332VLJ-5 Datasheet - Page 45

• Manufacturer Part Number: PC87332VLJ-5
• Description: PC87332VLJ (3.3V/5V) and PC87332VLJ-5 (5V) (SuperI/OTM III Premium Green) Floppy Disk Controller, Dual UARTs, IEEE1284 Parallel Port, and IDE Interfac
• Manufacturer: NSC [National Semiconductor]

4 0 FDC Command Set Description
4 1 15 Scan Commands
The Scan commands allow data read from the disk to be
compared against data sent from the P using ones com-
plement arithmetic sector by sector
There are three Scan commands to choose from
The results of these comparisons are indicated in the Status
Register bits 3 and 2 see Table 4-13 and the structure of
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
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
Register set (mimicking a Scan Equal Hit)
Scan Equal Disk Data
Scan Low
or Equal
Scan High
or Equal
Command
1 Scan Equal checks to see if the scanned value of the
disk data is equal to that of the P data The scan con-
dition is therefore disk 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 P
data The scan condition is therefore disk 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
TABLE 4-13 Scan Command Termination Values
P data The scan condition is therefore disk data
P data
Comparison
Disk Data
Disk Data
Condition
P Data
P Data
P Data
s
t
e
D3
Status
1
0
1
0
0
1
0
0
D2
0
1
0
0
1
0
0
1
e
P is used as a don’t care
Condition
P data
Met
Yes
Yes
Yes
Yes
Yes
No
No
No
Disk Data
Disk Data
Disk Data
Disk Data
Disk Data
Disk Data
Disk Data
Disk Data
Indicated
P Data
P Data
P Data
P Data
P Data
P Data
P Data
P Data
Result
s
data
k
l
l
k
e
i
e
e
t
(Continued)
45
SCAN EQUAL
Command Phase
Execution Phase Data transferred from system to control-
ler is compared to data read from disk
Result Phase
SCAN HIGH OR EQUAL
Command Phase
Execution Phase Data transferred from system to control-
ler is compared to data read from disk
Result Phase
MT
IPS
MT
IPS
MT
IPS
MFM
MFM
MFM
X
X
X
End of Track Sector Number
End of Track Sector Number
SK
SK
SK
X
X
X
Intersector Gap Length
Intersector Gap Length
Drive Head Number
Drive Head Number
Status Register 0
Status Register 1
Status Register 2
Status Register 0
Status Register 1
Status Register 2
Bytes per Sector
Sector Step Size
Bytes per Sector
Bytes per Sector
Sector Step Size
Bytes per Sector
Sector Number
Sector Number
Sector Number
Sector Number
Track Number
Track Number
Track Number
Track Number
Head Number
Head Number
1
X
1
X
1
X
0
X
1
X
1
X
HD
HD
HD
0
1
1
DR1
DR1
DR1
0
0
0
DR0
DR0
DR0
1
1
1