PC87307 Datasheet, PDF (101/218 Pages) National Semiconductor (TI) – PC87307/PC97307 Plug and Play Compatible and PC97 Compliant SuperI/O

If the number of tracks on the disk drive exceeds the maxi-
mum number of RECALIBRATE step pulses, it may be nec-
essary to issue another RECALIBRATE command.
TABLE 5-20. Maximum RECALIBRATE Step Pulses for
Values of R255 and ETR
R255 ETR
0
0
1
0
0
1
1
1
Maximum Number of
RECALIBRATE Step Pulses
85 (default)
255
3925
4095
The pulses actually occur while the controller is in the drive
polling phase. See “Drive Polling Phase” on page 80.
An interrupt is generated after the TRK0 signal is asserted,
or after the maximum number of RECALIBRATE step puls-
es is issued.
Software should ensure that the RECALIBRATE 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.
No command, except a SENSE INTERRUPT command,
should be issued while a RECALIBRATE command is in
progress.
Result Phase
None.
5.7.15 The RELATIVE SEEK Command
The RELATIVE SEEK command issues STEP pulses that
make the head of the selected drive step in or out a pro-
grammable number of tracks.
Command Phase
7
6
5
4
3
2
1
0
1 DIR 0
0
1
1
1
1
X
X
X
X
X HD DS1 DS0
Relative Track Number (RTN)
First Command Phase Byte, Opcode,
Bit - 6 Step Direction DIR
This bit defines the step direction.
0 - Step head out.
1 - Step head in.
Second Command Phase Byte
See “Second Command Phase Byte” on page 90 for a
description of the Drive Select (DS1,0) and Head Select
(HD) bits.
Third Command Phase Byte - Relative Track Number
(RTN)
This value specifies how many tracks the head should
step in or out from the current track.
Execution Phase
After the last command byte is issued, the Drive Busy bit for
the selected drive is set in the Main Status Register (MSR).
See bits 3-0 in Section 5.3.5 on page 74.
The controller waits the Delay Before Processing time (see
Table 5-25 on page 106) for the selected drive., and then
becomes idle. See “Idle Phase” on page 80.
Then, the controller enters the idle phase and issues RTN
STEP pulses until the TRK0 disk interface input signal be-
comes active or until the specified number (RTN) of STEP
pulses have been issued. After the RELATIVE SEEK oper-
ation is complete, the controller generates an interrupt.
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
and the SCAN HIGH OR EQUAL Commands
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:
• 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.
Command Phase
SCAN EQUAL
7
6
5
4
3
2
1
0
MT MFM SK 1
0
0
0
1
IPS X
X
X
X HD DS1 DS0
Track Number
Head Number
Sector Number
Bytes-Per-Sector Code
End of Track (EOT) Sector Number
Bytes Between Sectors - Gap 3
Sector Step Size
101
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