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.