data rate selected in the Data Rate Select
Register. The user must ensure that these two
data rates remain consistent.
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
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
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.
accommodate
this
head
activation
and
deactivation time, the Gap2 field is expanded to a
length of 41 bytes. The format field shown on
Page 58 illustrates the change in the Gap2 field
size for the perpendicular format.
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.
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.
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.
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
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.
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.
66
SMSC [ SMSC CORPORATION ]
