Note that if implied seek is not enabled, the read and
write commands should be preceded by:
SE
IC
INTERRUPT DUE TO
Polling
Normal termination of Seek
or Recalibrate command
Abnormal termination of
Seek or Recalibrate
command
0
1
11
00
1) Seek command - Step to the proper track
2) Sense Interrupt Status command - Terminate the
Seek command
3) Read ID - Verify head is on proper track
4) Issue Read/Write command.
1
01
Table 27 - Interrupt Identification
The Seek command does not have a result phase.
Therefore, it is highly recommended that the Sense
Interrupt Status command be 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 zero. Prior to issuing the POWERDOWN
command, it is highly recommended that the user service
all pending interrupts through the Sense Interrupt Status
command.
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.
Sense Drive Status
Sense Interrupt Status
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.
An interrupt signal on FINT pin is generated by the FDC
for one of the following reasons:
1. Upon entering the Result Phase of:
a. Read Data command
Specify
b. Read A Track command
c. Read ID command
d. Read Deleted Data command
e. Write Data command
f. Format A Track 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.
g. Write Deleted Data command
h. Verify command
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.
64
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