Sense Interrupt Status command is issued after
the Seek command to terminate it and to provide
verification of the head position (PCN). The H bit
(Head Address) in ST0 will always return to a "0".
When exiting POWERDOWN mode, the FDC
clears the PCN value and the status information to
The Seek, Relative Seek, and Recalibrate
commands have no result phase. The Sense
Interrupt Status command must be issued
immediately after these commands to terminate
them and to provide verification of the head
position (PCN). The H (Head Address) bit in ST0
will always return a "0". If a Sense Interrupt Status
is not issued, the drive will continue to be BUSY
and may affect the operation of the next
command.
zero.
Prior to issuing the POWERDOWN
command, it is highly recommended that the user
service all pending interrupts through the Sense
Interrupt Status command.
Sense Interrupt Status
Sense Drive Status
An interrupt signal on FINT pin is generated by the
FDC for one of the following reasons:
Sense Drive Status obtains drive status
information. It has not execution phase and goes
directly to the result phase from the command
phase. Status Register 3 contains the drive status
information.
1. Upon entering the Result Phase of:
a. Read Data command
b. Read A Track command
c. Read ID command
Specify
d. Read Deleted Data command
e. Write Data command
f. Format A Track command
g. Write Deleted Data command
h. Verify command
The Specify command sets the initial values for
each of the three internal times. The HUT (Head
Unload Time) defines the time from the end of the
execution phase of one of the read/write
commands to the head unload state. The SRT
(Step Rate Time) defines the time interval between
adjacent step pulses. Note that the spacing
between the first and second step pulses may be
shorter than the remaining step pulses. The HLT
(Head Load Time) defines the time between when
the Head Load signal goes high and the read/write
operation starts. The values change with the data
rate speed selection and are documented in
TABLE 31. The values are the same for MFM
and FM.
2. End of Seek, Relative Seek, or Recalibrate
command
3. FDC requires a data transfer during the
execution phase in the non-DMA mode
The Sense Interrupt Status command resets the
interrupt signal and, via the IC code and SE bit of
Status Register 0, identifies the cause of the
interrupt.
TABLE 30 - INTERRUPT IDENTIFICATION
SE
IC
INTERRUPT DUE TO
0
1
11
00
Polling
TABLE 31 - DRIVE CONTROL DELAYS (MS)
Normal termination of Seek
or Recalibrate command
Abnormal termination of
Seek or Recalibrate
command
1
01
HUT
SRT
500K 300K 250K
2M
1M
500K 300K 250K
2M
1M
0
1
64
4
128
8
256
16
426
26.7
512
32
4
3.75
8
7.5
16
15
26.7
25
32
30
65
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