FDC37C78-HT View Datasheet(PDF) - Microchip Technology
Part Name
Description
Manufacturer
FDC37C78-HT Datasheet PDF : 82 Pages
| |||
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.
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.
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:
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.
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 nTR0 pin from the FDD.
As long as the nTR0 pin is low, the DIR pin
remains 0 and step pulses are issued. When the
nTR0 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
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
3) Read ID - Verify head is on proper track
51
Share Link: 