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.
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.
When both GAP and WGATE bits of the
PERPENDICULAR MODE COMMAND are both
programmed to "0" (Conventional mode), then
D0, D1, D2, D3, and D4 can be programmed
independently to "1" for that drive to be set
automatically to Perpendicular mode. In this
mode the following set of conditions also apply:
1. The GAP2 written to a perpendicular drive
during a write operation will depend upon the
programmed data rate.
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 as shown on page 57. 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).
2. The write pre-compensation given to
perpendicular mode drive will be 0ns.
a
3. For D0-D3 programmed to "0" for
conventional mode drives any data written
will be at the currently programmed write
pre-compensation.
Note: Bits D0-D3 can only be overwritten when
OW is programmed as a "1".If either
GAP or WGATE is a "1" then D0-D3 are
ignored.
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.
Software and hardware resets have the
following effect on the PERPENDICULAR
MODE COMMAND:
1. "Software" resets (via the DOR or DSR
registers) will only clear GAP and WGATE
bits to "0". D0-D3 are unaffected and retain
their previous value.
2. "Hardware" resets will clear all bits
(GAP, WGATE and D0-D3) to "0", i.e all
conventional mode.
64
SMSC [ SMSC CORPORATION ]
