FDC37C665IR SMSC Corporation, FDC37C665IR Datasheet - Page 70

• Manufacturer Part Number: FDC37C665IR
• Description: 3/5 Volt Advanced High-Performance Multi-Mode Parallel Port Super I/O Floppy Disk Controller with Infranred Support
• Manufacturer: SMSC Corporation

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.
command, the length of the Gap2 field and VCO
enable timing can be altered to accommodate
the unique requirements of these drives. Table
31 describes the effects of the WGATE and
GAP bits for the Perpendicular Mode command.
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.
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
field shown on page 66 illustrates the change in
the Gap2 field size for the perpendicular format.
Upon a reset, the FDC will default to the
With this
In the
70
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
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.
then writes a new sync field, data address mark,
data field, and CRC as shown in Figure 4. 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.
(WGATE = 1, GAP = 1), 38 bytes will be written
in the Gap2 space.
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.
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
enhancement allows data transfers between
Conventional and Perpendicular drives without
having to issue Perpendicular mode commnds
between the accesses of the different drive
types,
compensation values.
For the 1 Mbps perpendicular mode
nor
PLL
having
VCO
recording
to
Since the bit density is
is
change
enabled
The information
drives.
The controller
write
(VCOEN)
This
pre-