LPC47M182 datasheet(71/223 Pages) SMSC

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Advanced I/O Controller with Motherboard GLUE Logic

Datasheet

SMSC LPC47M182

Revision 1.8 SMSC/Non-SMSC Register Sets (02-24-05)

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:

Direction signal to drive set to “1” (step in) and issues step pulses.

PCN > NCN:

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

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