Table 31 - Effects of WGATE and GAP Bits
LENGTH OF
GAP2 FORMAT
FIELD
PORTION OF GAP 2
WRITTEN BY WRITE
DATA OPERATION
WGATE
GAP
MODE
0
0
0
1
Conventional
Perpendicular
(500 Kbps)
Reserved
(Conventional)
Perpendicular
(1 Mbps)
22 Bytes
22 Bytes
0 Bytes
19 Bytes
1
1
0
1
22 Bytes
41 Bytes
0 Bytes
38 Bytes
LOCK
ENHANCED DUMPREG
In order to protect systems with long DMA
latencies against older application software that
can disable the FIFO, the LOCK Command has
been added. This command should only be
used by the FDC routines, and application
software should refrain from using it. If an
application calls for the FIFO to be disabled
then the CONFIGURE command should be
used.
The DUMPREG command is designed to
support system run-time diagnostics and
application software development and debug.
To accommodate the LOCK command and the
enhanced PERPENDICULAR MODE command
the eighth byte of the DUMPREG command has
been modified to contain the additional data
from these two commands.
COMPATIBILITY
The LOCK command defines whether the
EFIFO, FIFOTHR, and PRETRK parameters of
the CONFIGURE command can be RESET by
the DOR and DSR registers. When the LOCK
bit is set to logic "1" all subsequent "software
RESETS by the DOR and DSR registers will not
change the previously set parameters to their
default values. All "hardware" RESET from the
RESET pin will set the LOCK bit to logic "0" and
return the EFIFO, FIFOTHR, and PRETRK to
their default values. A status byte is returned
immediately after issuing a a LOCK command.
This byte reflects the value of the LOCK bit set
by the command byte.
The FDC37C93xFR was designed with software
compatibility in mind. It is a fully backwards-
compatible solution with the older generation
765A/B disk controllers.
implements on-board registers for compatibility
with the PS/2, as well as PC/AT and PC/XT,
The FDC also
floppy disk controller subsystems. After
a
hardware reset of the FDC, all registers,
functions and enhancements default to a PC/AT,
PS/2 or PS/2 Model 30 compatible operating
mode, depending on how the IDENT and MFM
bits are configured by the system BIOS.
68
SMSC [ SMSC CORPORATION ]
