Advanced I/O Controller with Motherboard GLUE Logic
Datasheet
6.18 Control Commands
Control commands differ from the other commands in that no data transfer takes place. Three commands
generate an interrupt when complete: Read ID, Recalibrate, and Seek. The other control commands do
not generate an interrupt.
6.18.1 Read ID
The Read ID command is used to find the present position of the recording heads. The FDC stores the
values from the first ID field it is able to read into its registers. If the FDC does not find an ID address mark
on the diskette after the second occurrence of a pulse on the nINDEX pin, it then sets the IC code in
Status Register 0 to “01” (abnormal termination), sets the MA bit in Status Register 1 to “1”, and terminates
the command.
The following commands will generate an interrupt upon completion. They do not return any result bytes.
It is highly recommended that control commands be followed by the Sense Interrupt Status command.
Otherwise, valuable interrupt status information will be lost.
6.18.2 Recalibrate
This command causes the read/write head within the FDC to retract to the track 0 position. The FDC
clears the contents of the PCN counter and checks the status of the nTRK0 pin from the FDD. As long as
the nTRK0 pin is low, the DIR signal remains 0 and step pulses are issued. When the nTRK0 pin goes
high, the SE bit in Status Register 0 is set to “1” and the command is terminated. If the nTRK0 pin is still
low after 255 step pulses have been issued, the FDC sets the SE and the EC bits of Status Register 0 to
“1” and terminates the command. Disks capable of handling more than 256 tracks per side may require
more than one Recalibrate command to return the head back to physical Track 0.
The Recalibrate command does not have a result phase. The Sense Interrupt Status command must be
issued after the Recalibrate command to effectively terminate it and to provide verification of the head
position (PCN). During the command phase of the recalibrate operation, the FDC is in the BUSY state, but
during the execution phase it is in a NON-BUSY state. At this time, another Recalibrate command may be
issued, and in this manner parallel Recalibrate operations may be done on up to four drives at once. Upon
power up, the software must issue a Recalibrate command to properly initialize all drives and the
controller.
6.18.3 Seek
The read/write head within the drive is moved from track to track under the control of the Seek command.
The FDC compares the PCN, which is the current head position, with the NCN and performs the following
operation if there is a difference:
PCN < NCN:
PCN > NCN:
Direction signal to drive set to “1” (step in) and issues step pulses.
Direction signal to drive set to “0” (step out) and issues step pulses.
The rate at which step pulses are issued is controlled by SRT (Stepping Rate Time) in the Specify
command. After each step pulse is issued, NCN is compared against PCN, and when NCN = PCN the SE
bit in Status Register 0 is set to “1” and the command is terminated. During the command phase of the
seek or recalibrate operation, the FDC is in the BUSY state, but during the execution phase it is in the
SMSC LPC47M182
71
Revision 1.8 SMSC/Non-SMSC Register Sets (02-24-05)
DATASHEET
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