PC87307VUL National Semiconductor, PC87307VUL Datasheet - Page 102

• Manufacturer Part Number: PC87307VUL
• Description: PC87307/PC97307 Plug and Play Compatible and PC97 Compliant SuperI/O
• Manufacturer: National Semiconductor

www.national.com
SCAN LOW OR EQUAL
SCAN HIGH OR EQUAL
First through Eighth Command Phase Bytes -
All Scan Commands
See READ DATA command for a description of the first
eight command phase bytes.
Ninth Command Phase Byte, Sector Step Size
During execution, the value of this byte is added to the cur-
rent sector number to determine the next sector to read.
Execution Phase
The most significant bytes of each sector are compared
first. If wildcard mode is enabled in bit 4 of the fourth com-
mand phase byte in the MODE command (page 94), a value
of FFh from either the disk or the microprocessor always
causes a match.
After each sector is read, if there is no match, the next sec-
tor is read. The next sector is the current sector number plus
the Sector Step Size specified in the ninth command phase
byte.
The scan operation continues until the condition is met, the
End of Track (EOT) is reached or the Terminal Count (TC)
signal becomes active.
Read error conditions during scan commands are the same
as read error conditions during the execution phase of the
READ DATA command. See page 97.
If the Skip Control (SK) bit is set to 1, sectors with deleted
data marks are ignored.
IPS
IPS
MT
MT
7
7
MFM
MFM
X
X
6
6
End of Track (EOT) Sector Number
End of Track (EOT) Sector Number
Bytes Between Sectors - Gap 3
Bytes Between Sectors - Gap 3
SK
SK
X
X
5
Bytes-Per-Sector Code
5
Bytes-Per-Sector Code
Sector Step Size
Sector Step Size
Sector Number
Sector Number
Track Number
Track Number
Head Number
Head Number
X
X
4
1
4
1
X
X
3
1
3
1
HD
HD
2
0
2
1
DS1
DS1
1
0
1
0
DS0
DS0
0
1
0
1
102
If all sectors read are skipped, the command terminates
with bit 3 of ST2 set to 1, i.e., disk data equals microproces-
sor data.
Result Phase
Table 5-21 shows how all the scan commands affect bits
3,2 of the Status 2 (ST2) result phase register. See “Result
Phase Status Register 2 (ST2)” on page 82.
TABLE 5-21. The Effect of Scan Commands on the ST2
5.7.17 The SEEK Command
The SEEK command issues pulses of the STEP signal to
the selected drive, to move it in or out until the desired track
number is reached.
Software should ensure that the 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. See “Digital Out-
put Register (DOR), Offset 02h” on page 71.
No command, except a SENSE INTERRUPT command,
should be issued while a SEEK command is in progress.
SCAN HIGH
SCAN LOW
OR EQUAL
OR EQUAL
Command
7
EQUAL
SCAN
6
Result Phase Status Register 0 (ST0)
Result Phase Status Register 1 (ST1)
Result Phase Status Register 2 (ST2)
Bit 3 - Scan
Satisfied
5
Bytes-Per-Sector Code
Result Phase Status
Register 2 (ST2)
1
0
1
0
0
1
0
0
Sector Number
Track Number
Head Number
Register
4
Not Satisfied
Bit 2 - Scan
3
0
1
0
0
1
0
0
1
2
Condition
Disk = P
Disk = P
Disk < P
Disk > P
Disk = P
Disk > P
Disk < P
Disk
1
0
P