Table 2 -- Main Status Register
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bit 0        Drive 0 busy seeking
bit 1        Drive 1 busy seeking
bit 2        Drive 2 busy seeking
bit 3        Drive 3 busy seeking
bit 4        FDC Busy doing a command (other than seek)
bit 5        Non-DMA mode
bit 6        DIO: Data Input/Output (1 = input)
bit 7        RQM: Request for Master (1 = ready for transfer)