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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 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.
ENHANCED DUMPREG
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 FDC37C957FR 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, 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.
Parallel Port Floppy Disk Controller
Refer to the the Parallel Port Section for details.
Hot Swapable 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.