
69
Sense Interrupt Status
An interrupt signal is generated by the FDC for one of the following reasons:
1. Upon entering the Result Phase of:
a. Read Data command
b. Read A Track command
c. Read ID command
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.
Table 24 – Interrupt Identification
IC
11
00
Normal termination of Seek or
Recalibrate command
Abnormal termination of Seek or
Recalibrate command
SE
0
1
INTERRUPT DUE TO
Polling
1
01
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 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.
Specify
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 26. The values are the same for MFM and FM.