Table 1 - Digital-Output Register (DOR)
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bits 0 & 1     a two bit field for drive select
bit 2          NOT reset: if clear, card is held reset
bit 3          permit Interrupt 6 and DMA requests from card
bit 4          floppy drive 0 ('A') motor on
bit 5          floppy drive 1 ('B') motor on
bit 6          floppy drive 2 motor on (not usually used in PC)
bit 7          floppy drive 3 motor on (not usually used in PC)

Note: to reset card, output a zero to the DOR, then output 0x0C (bits two
and three set).  This will set and release the "reset" signal  and allow
interrupts and DMA, but not select a drive or turn a motor on.

Note: to select a drive, the drive number is in binary should be placed
in bits 0 & 1.  e.g., drive 1 would be bit 0 set and bit 1 clear.