FDC37M817-MS Standard Microsystems (SMSC), FDC37M817-MS Datasheet - Page 65

• Manufacturer Part Number: FDC37M817-MS
• Manufacturer: Standard Microsystems (SMSC)

Specifications of FDC37M817-MS

• Pin Count: 100
• Lead Free Status / RoHS Status: Compliant

counting from 0 again as the track number goes
above 255 (D). It is the user's 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 "extended track area" (greater than
255). Any command issued will use the current
PCN value except for the Recalibrate command,
which only looks for the TRACK0 signal.
Recalibrate will return an error if the head is farther
than 79 due to its limitation of issuing a maximum
of 80 step pulses. The user simply needs to issue
a second Recalibrate command.
command and implied seeks will function correctly
within the 44 (D) track (299-255) area of the
"extended track area". It is the user's 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.
commands will return different cylinder results
which may be difficult to keep track of with
software without the Read ID command.
Different FDC
The Seek
65
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 28
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.
recording density.
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.
accommodate
deactivation time, the Gap2 field is expanded to a
length of 41 bytes. The
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
This works out to about 38 bytes at a 1 Mbps
this
Whenever the write head is
head
Format
activation
Fields table
With this
and
To