82091AA Datasheet, PDF (153/204 Pages) Intel Corporation – ADVANCED INTEGRATED PERIPHERAL (AIP)

82091AA
8 5 3 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
8 5 3 1 READ ID Command
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 INDEX 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 termi-
nates the command
The following commands will generate an interrupt
upon completion They do not return any result
bytes It is recommended that control commands be
followed by the SENSE INTERRUPT STATUS Com-
mand Otherwise valuable interrupt status informa-
tion will be lost
8 5 3 2 RECALIBRATE Command
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 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 FDC
sets the SE and the EC bits of Status Register 0 to 1
and terminates the command Disks capable of han-
dling 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 re-
sult phase The SENSE INTERRUPT STATUS Com-
mand must be issued after the RECALIBRATE Com-
mand to effectively terminate it and to provide verifi-
cation of the head position (PCN) During the com-
mand 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 RECALI-
BRATE Command may be issued and in this man-
ner parallel RECALIBRATE operations may be
done on up to 2 drives simultaneously
After powerup software must issue a RECALI-
BRATE Command to properly initialize all drives and
the controller
8 5 3 3 DRIVE SPECIFICATION Command
The FDC uses two pins DRVDEN0 and DRVDEN1
to select the density for modern drives These sig-
nals inform the drive of the type of diskette in the
drive The DRIVE SPECIFICATION Command speci-
fies the polarity of the DRVDEN0 and DRVDEN1
pins It also enables disables DSR programmed pre-
compensation
This command removes the need for a hardware
work-around to accommodate differing specifica-
tions among drives By programming this command
during BIOS’s POST routine the floppy disk control-
ler internally configures the correct values for
DRVDEN0 and DRVDEN1 with corresponding pre-
compensation value and data rate table enabled for
the particular type of drive
This command is protected from software resets Af-
ter executing the DRIVE SPECIFICATION Com-
mand subsequent software resets will not clear the
programmed parameters Only another DRIVE
SPECIFICATION Command or hard reset can reset
it to default values The 6 LSBs of the last byte of
this command are reserved for future use
The DRATE0 and DRATE1 are values as pro-
grammed in the DSR register See Table 32 for pin
decoding at different data rates
Table 32 describes the drives that are supported
with the DT0 DT1 bits of the DRIVE SPECIFICA-
TION Command
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