NAME   rev ADDR type chip Description
---------------------------------------------------------------------------
DSKLEN	024 W		P    Disk length

	 This register contains the length (number of words) of
	 disk DMA data. It also contains 2 control bits. These
 	 are a DMA enable bit, and a DMA direction (read/write) bit.

         +------+----------+------------------------------------+
         | BIT# | FUNCTION | DESCRIPTION                        |
         +------+----------+------------------------------------+
         | 15   | DMAEN    | Disk DMA enable                    |
         | 14   | WRITE    | Disk write (RAM or disk) if 1      |
         | 13-0 | LENGTH   | Length (# of words) of DMA data.   |
         +------+----------+------------------------------------+