82091AA Datasheet, PDF (157/204 Pages) Intel Corporation – ADVANCED INTEGRATED PERIPHERAL (AIP)

82091AA
8 5 3 9 VERSION Command
The VERSION Command checks to see if the con-
troller is an enhanced type (82077 82077AA
82077SL) or the older type (8272A 765A) A value
of 90h is returned as the result byte defining an en-
hanced FDD controller is in use No interrupts are
generated
8 5 3 10 RELATIVE SEEK Command
The RELATIVE SEEK Command is coded the same
as for the SEEK Command except for the MSB of
the first byte and the DIR bit
DIR Head Step Direction Control
DIR
ACTION
0
Step Head Out
1
Step Head In
RCN Relative Cylinder Number that determines
how many tracks to step the head in or out
from the current track number
The RELATIVE SEEK Command differs from the
SEEK Command in that it steps the head the abso-
lute number of tracks specified in the command in-
stead of making a comparison against an internal
register The SEEK Command is good for drives that
support a maximum of 256 tracks RELATIVE
SEEKs cannot be overlapped with other RELATIVE
SEEKs Only one RELATIVE SEEK can be active at
a time Bit 4 of Status Register 0 (EC) will be set to 1
if RELATIVE SEEK attempts to step outward beyond
Track 0
As an example assume that a floppy drive has 300
useable tracks and that the host needs to read track
300 and the head is on any track (0–255) If a SEEK
Command is issued the head stops at track 255 If a
RELATIVE SEEK Command is issued the FDC
moves the head the specified number of tracks re-
gardless of the internal cylinder position register (but
increments the register) If the head had been on
track 40 (D) the maximum track that the FDC could
position the head on using RELATIVE SEEK is 296
(D) the initial track ^a256 (D) The maximum count
that the head can be moved with a single RELATIVE
SEEK Command is 256 (D)
The internal register PCN would overflow as the
cylinder number crossed track 255 and would con-
tain 40 (D) The resulting PCN value is thus (NCN ^a
PCN) mod 256 Functionally the FDC starts count-
ing from 0 again as the track number goes above
255(D) It is the users responsibility to compensate
FDC functions (precompensation track number)
when accessing tracks greater than 255 The FDC
does not keep track that it is working in an ‘‘extend-
ed track area’’ (greater than 255) Any command is-
sued uses the current PCN value except for the RE-
CALIBRATE Command that only looks for the
TRACK0 signal RECALIBRATE returns an error if
the head is farther than 79 due to its limitation of
issuing a maximum 80 step pulses The user simply
needs to issue a second RECALIBRATE Command
The SEEK Command and implied seeks function
correctly within the 44 (D) track (299 – 255) area of
the extended track area It is the users responsibility
not to issue a new track position that exceeds the
maximum track that is present in the extended area
To return to the standard floppy range (0 – 255) of
tracks a RELATIVE SEEK is issued to cross the
track 255 boundary
A RELATIVE SEEK Command can be used instead
of the normal SEEK Command but the host is re-
quired to calculate the difference between the cur-
rent head location and the new (target) head loca-
tion This may require the host to issue a READ ID
Command to ensure that the head is physically on
the track that software assumes it to be Different
FDC commands return different cylinder results
which may be difficult to keep track of with software
without the READ ID Command
8 5 3 11 DUMPREG Command
The DUMPREG Command is designed to support
system run-time diagnostics and application soft-
ware development and debug The command re-
turns pertinent information regarding the status of
many of the programmed fields in the FDC This can
be used to verify the values initialized in the FDC
8 5 3 12 PERPENDICULAR MODE Command
An added capability of the FDC is the ability to inter-
face directly to perpendicular recording floppy
drives Perpendicular recording differs from the tradi-
tional longitudinal method by orienting the magnetic
bits vertically This scheme packs in more data bits
for the same area
The PERPENDICULAR MODE Command allows the
system designers to designate specific drives as
Perpendicular recording drives Data transfers be-
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