Note that if implied seek is not enabled, the read
and write commands should be preceded by:
Table 27 - Interrupt Identification
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
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
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.
d. Read Deleted Data command
e. Write Data command
f. Format A Track command
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.
65
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