The disk controller can issue three kinds of interrupts:

   *   DSKSYNC  (level 5,  INTREQ  bit 12) -- input stream matches the
                                             DSKSYNC register.
   *   DSKBLK  (level 1,  INTREQ  bit 1) -- disk DMA has completed.
   *   INDEX  (level 6, 8520 Flag pin) -- index sensor triggered.

Interrupts are explained further in the section
 Length, Direction, DMA Enable .

See Chapter 7, "System Control Hardware," for more information about
  interrupts .

See  Appendix F  for more information on the 8520.