
SMSC DS – FDC37N958FR
Page 77
Rev. 09/01/99
Table 36 - Effects of WGATE and GAP Bits
LENGTH OF GAP2
FORMAT FIELD
Conventional
Perpendicular
(500 Kbps)
Reserved
(Conventional)
Perpendicular
(1 Mbps)
WGATE
0
0
GAP
0
1
MODE
PORTION OF GAP 2 WRITTEN BY
WRITE DATA OPERATION
0 Bytes
19 Bytes
1
1
0
1
22 Bytes
22 Bytes
22 Bytes
41 Bytes
0 Bytes
38 Bytes
LOCK
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 LOCK command
defines whether the EFIFO, FIFOTHR, and
PRETRK
parameters
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.
of
the
CONFIGURE
ENHANCED DUMPREG
The DUMPREG command is designed to support
system run-time diagnostics and application
software
development
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.
and
debug.
To
COMPATIBILITY
The FDC37N958FR was designed with software
compatibility in mind. It is a fully backwards-
compatible solution with the older generation
765A/B disk controllers. The FDC also
implements on-board registers for compatibility
with the PS/2, as well as PC/AT and PC/XT, FDC
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.
Parallel Port FDC
Refer to the the Parallel Port Section for details.
Hot Swappable FDD Capability
The FDC output pins will tri-state whenever the
FDC Logical Device is powered-down or not
activated. In addition setting bit 7 of the FDD
Mode Configuration register (LD0_CRF0) will tri-
state the FDC output pins. Bit 7 only affects the
standard FDC interface, it has no effect on the
Parallel Port Floppy Interface.