82077AA Datasheet, PDF (30/62 Pages) Intel Corporation – CHMOS SINGLE-CHIP FLOPPY DISK CONTROLLER

82077AA
5 2 Control Commands
Control commands differ from the other commands
in that no data transfer takes place Three com-
mands generate an interrupt when complete READ
ID RECALIBRATE and SEEK The other control
commands do not generate an interrupt
5 2 1 READ ID
The READ ID command is used to find the present
position of the recording heads The 82077AA
stores the values from the first ID Field it is able to
read into its registers If the 82077AA does not find
an ID Address Mark on the diskette after the second
occurrence of a pulse on the IDX pin it then sets the
IC code in Status Register 0 to ‘‘01’’ (Abnormal ter-
mination) 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 com-
mands be followed by the SENSE INTERRUPT
STATUS command Otherwise valuable interrupt
status information will be lost
5 2 2 RECALIBRATE
This command causes the read write head within
the 82077AA to retract to the track 0 position The
82077AA clears the contents of the PCN counter
and checks the status of the TRK0 pin from the
FDD As long as the TRK0 pin is low the DIR pin
remains 0 and step pulses are issued When the
TRK0 pin goes high the SE bit in Status Register 0
is set to ‘‘1’’ and the command is terminated If the
TRK0 pin is still low after 79 step pulses have been
issued the 82077AA sets the SE and the EC bits of
Status Register 0 to ‘‘1’’ and terminates the com-
mand Disks capable of handling more than 80
tracks per side may require more than one RECALI-
BRATE command to return the head back to physi-
cal Track 0
The RECALIBRATE command does not have a re-
sult phase 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 82077AA is in
the BUSY state but during the execution phase it is
in a NON BUSY state At this time another RECALI-
BRATE command may be issued and in this man-
ner parallel RECALIBRATE operations may be
done on up to 4 drives at once
Upon power up the software must issue a RECALI-
BRATE command to properly initialize all drives and
the controller
5 2 3 SEEK
The read write head within the drive is moved from
track to track under the control of the SEEK Com-
mand The 82077AA compares the PCN which is the
current head position with the NCN and performs
the following operation if there is a difference
PCN ^k NCN Direction signal to drive set to ‘‘1’’
(step in) and issues step pulses
PCN ^l NCN Direction signal to drive set to ‘‘0’’
(step out) and issues step pulses
The rate at which step pulses are issued is con-
trolled by SRT (Stepping Rate Time) in the SPECIFY
command After each step pulse is issued NCN is
compared against PCN and when NCN ^e PCN
then the SE bit in Status Register 0 is set to ‘‘1’’ and
the command is terminated
During the command phase of the seek or recali-
brate operation the 82077AA is in the BUSY state
but during the execution phase it is in the NON
BUSY state
30