pc87317vul National Semiconductor Corporation, pc87317vul Datasheet - Page 128

• Manufacturer Part Number: pc87317vul
• Description: Pc87317vul/pc97317vul Superi/o Plug And Play Compatible With Acpi Compliant Controller/extender
• Manufacturer: National Semiconductor Corporation

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Software should ensure that the RELATIVE SEEK com-
mand is issued for only one drive at a time. This is because
the drives are actually selected via the Digital Output Reg-
ister (DOR), which can only select one drive at a time.
No command, except the SENSE INTERRUPT command,
should be issued while a RELATIVE SEEK command is in
progress.
Result Phase
None.
5.7.16 The SCAN EQUAL, the SCAN LOW OR EQUAL
The scan commands compare data read from the disk with
data sent from the microprocessor. This comparison pro-
duces a match for each scan command, as follows, and as
shown in TABLE 5-21 "The Effect of Scan Commands on
the ST2 Register" on page 129:
Command Phase
SCAN EQUAL
SCAN LOW OR EQUAL
IPS
IPS
MT
MT
7
7
SCAN EQUAL - Disk data equals microprocessor da-
ta.
SCAN LOW OR EQUAL - Disk data is less than or
equal to microprocessor data.
SCAN HIGH OR EQUAL - Disk data is greater than or
equal to microprocessor data.
and the SCAN HIGH OR EQUAL Commands
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
5
Bytes-Per-Sector Code
Bytes-Per-Sector Code
Sector Step Size
Sector Step Size
Sector Number
Sector Number
Track Number
Head Number
Track Number
Head Number
X
X
4
1
4
1
X
X
3
0
3
1
HD
HD
2
0
2
0
DS1
DS1
1
0
1
0
DS0
DS0
0
1
0
1
128
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 ( "Bit 4 - Scan
Wild Card (WLD)" on page 120), 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 sector
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 Section 5.7.10 "The READ
DATA Command" on page 122.
If the Skip Control (SK) bit is set to 1, sectors with deleted
data marks are ignored. If all sectors read are skipped, the
command terminates with bit 3 of ST2 set to 1, i.e., disk data
equals microprocessor data.
Result Phase
IPS
MT
7
7
MFM
X
6
6
Result Phase Status Register 0 (ST0)
Result Phase Status Register 1 (ST1)
Result Phase Status Register 2 (ST2)
End of Track (EOT) Sector Number
Bytes Between Sectors - Gap 3
SK
X
5
5
Bytes-Per-Sector Code
Bytes-Per-Sector Code
Sector Step Size
Sector Number
Sector Number
Track Number
Head Number
Track Number
Head Number
X
4
1
4
X
3
1
3
HD
2
1
2
DS1
1
0
1
DS0
0
1
0