5. IDE Command Descriptions
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OPERATIONS DESCRIPTION
The following pages describe operations that span several of the commands covered in
the preceding section.
Reset
A reset condition will set the drive busy, allowing the drive to perform the proper
initialization required for normal operation. A reset condition can be generated in four
ways. There are two hardware resets, one from the host and one from the drive power
sense circuitry. These are set high when the system and the drive, respectively,
acknowledge good power. The other two resets are software generated. The host can
write to the digital output register and set the reset bit. The host software reset condition
will persist until the reset bit is written to a zero. The drive microprocessor can set reset
through a write to a register. The drive processor reset is valid for one cycle and like all
other resets is ORed together to generate the signals that initialize the hardware.
Once the reset has been removed and the drive has been re-enabled, with BSY still
active, the drive will perform any necessary hardware initialization, clear any previously
programmed drive parameters, revert to the defaults, load the command block registers
with their initial values, and reset BSY. No interrupt is generated when initialization is
complete.
Initial values for the command block registers areas are as follows:
Error Register
01h
Sector Count
01h
Sector Number
01h
Cylinder Low
00h
Cylinder High
00h
Drive/Head Register
00h
BSY Operation
The latch holding BSY is set in a number of ways. A reset condition as described above
is one way. Another method occurs when the host issues a command. For a read type
command, the register is clocked BSY on the host write of the command register. The
disk controller and microprocessor prepare the data to return and set the drive not busy
to allow the host access to the data requested.
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