LPC47M182 SMSC Corporation, LPC47M182 Datasheet - Page 75

• Manufacturer Part Number: LPC47M182
• Description: ADVANCED I/O CONTROLLER WITH MOTHERBOARD GLUE LOGIC
• Manufacturer: SMSC Corporation

Advanced I/O Controller with Motherboard GLUE Logic
Datasheet
6.25
SMSC LPC47M182
responsibility not to issue a new track position that will exceed the maximum track that is present in the
extended area.
To return to the standard floppy range (0-255) of tracks, a Relative Seek should be issued to cross the
track 255 boundary.
A Relative Seek can be used instead of the normal Seek, but the host is required to calculate the
difference between the current head location and the new (target) head location. 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 will return different cylinder results which may be difficult to keep track
of with software without the Read ID command.
Perpendicular Mode
The Perpendicular Mode command should be issued prior to executing Read/Write/Format commands that
access a disk drive with perpendicular recording capability. With this command, the length of the Gap2
field and VCO enable timing can be altered to accommodate the unique requirements of these drives.
Table 6.27 describes the effects of the WGATE and GAP bits for the Perpendicular Mode command.
Upon a reset, the FDC will default to the conventional mode (WGATE = 0, GAP = 0).
Selection of the 500 Kbps and 1 Mbps perpendicular modes is independent of the actual data rate
selected in the Data Rate Select Register. The user must ensure that these two data rates remain
consistent.
The Gap2 and VCO timing requirements for perpendicular recording type drives are dictated by the design
of the read/write head. In the design of this head, a pre-erase head precedes the normal read/write head
by a distance of 200 micrometers. This works out to about 38 bytes at a 1 Mbps recording density.
Whenever the write head is enabled by the Write Gate signal, the pre-erase head is also activated at the
same time. Thus, when the write head is initially turned on, flux transitions recorded on the media for the
first 38 bytes will not be preconditioned with the pre-erase head since it has not yet been activated. To
accommodate this head activation and deactivation time, the Gap2 field is expanded to a length of 41
bytes. The Format Fields table illustrates the change in the Gap2 field size for the perpendicular format.
On the read back by the FDC, the controller must begin synchronization at the beginning of the sync field.
For the conventional mode, the internal PLL VCO is enabled (VCOEN) approximately 24 bytes from the
start of the Gap2 field. But, when the controller operates in the 1 Mbps perpendicular mode (WGATE = 1,
GAP = 1), VCOEN goes active after 43 bytes to accommodate the increased Gap2 field size. For both
cases, and approximate two-byte cushion is maintained from the beginning of the sync field for the
purposes of avoiding write splices in the presence of motor speed variation.
For the Write Data case, the FDC activates Write Gate at the beginning of the sync field under the
conventional mode. The controller then writes a new sync field, data address mark, data field, and CRC.
With the pre-erase head of the perpendicular drive, the write head must be activated in the Gap2 field to
insure a proper write of the new sync field. For the 1 Mbps perpendicular mode (WGATE = 1, GAP = 1),
38 bytes will be written in the Gap2 space. Since the bit density is proportional to the data rate, 19 bytes
will be written in the Gap2 field for the 500 Kbps perpendicular mode (WGATE = 1, GAP =0).
It should be noted that none of the alterations in Gap2 size, VCO timing, or Write Gate timing affect normal
program flow. The information provided here is just for background purposes and is not needed for normal
operation. Once the Perpendicular Mode command is invoked, FDC software behavior from the user
standpoint is unchanged.
The perpendicular mode command is enhanced to allow specific drives to be designated Perpendicular
recording drives. This enhancement allows data transfers between Conventional and Perpendicular drives
without having to issue Perpendicular mode commands between the accesses of the different drive types,
nor having to change write pre-compensation values.
DATASHEET
75
Revision 1.8 SMSC/Non-SMSC Register Sets (02-24-05)