There are occasions when the floppy controller designed onto the motherboard of a system needs to be disabled in order to operate another floppy controller on the expansion bus. This can be done without changing the BIOS or remapping the address of the floppy controller (provided there is a Jumper, or another way to disable the chipselect on the native controller).
Upon reset theDOR register in the 82078 is set to 00H. If the CS# is left enabled during the POST, the DOR is set to 0CH, this enables the DMA GATE # bit in the DOR. When this bit is set the 82078 treats a DACK# and a RD# or WR# as an internal chip select (CS#). Bus contention will occur between the native controller and the auxiliary controller if the DMA GATE# bit becomes active, even if the CS # signal is not present.
The proper way to disable the native floppy controller is to disable the CS# before the system is turned on. This will prevent the native controller from get ting initialized. Another option is map the native controller to a secondary address space, then disable the DMA GATE # via the DOR disabling the DMA GATE #. This assumes that the native controller is switchable to a secondary address space.