NAME   rev ADDR type chip Description
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DSKPTH h 020 W  A	Disk pointer (high 5 bits) (old-3 bits)
DSKPTL   022 W  A	Disk pointer (low 15 bits)

		This pair of registers contains the 20 bit address
		of disk DMA data. These address registers must be
		initalized by the processor or coprocessor
		before disk DMA is enabled.