LPC47N227TQFP Standard Microsystems (SMSC), LPC47N227TQFP Datasheet - Page 61

• Manufacturer Part Number: LPC47N227TQFP
• Manufacturer: Standard Microsystems (SMSC)

Specifications of LPC47N227TQFP

• Lead Free Status / RoHS Status: Not Compliant

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.
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.
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 pin 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 nTR0 pin is still low after
79 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 80 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.
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:
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
NON-BUSY state. At this time, another Seek or Recalibrate command may be issued, and in this manner,
parallel seek operations may be done on up to four drives at once.
Note that if implied seek is not enabled, the read and write commands should be preceded by:
1) Seek command - Step to the proper track
2) Sense Interrupt Status command - Terminate the Seek command
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.
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