DSKLEN

          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.   |
         +------+----------+------------------------------------+