c $FE56 sets interrupt mode 2 with high order byte of $09
C $FE56 set I to $09 for the high byte of the address to which control is transferred on an interrupt
C $FE5A set interrupt mode 2
C $FE5C return

C $FE60 load I with $3E - don't know why since my Z80 reference guide makes no mention of it!
C $FE64 set interrupt mode so that $0038 is called when an interrupt occurs (i.e. real-time clock is incremented and the keyboard is scanned)
C $FE66 return


C $FE69 disable interrupts
C $FE6A call $DF0C which executes a jump to $DF72
C $FE6D enable interrupts
C $FE6E jump to $0038 in ROM to increment real-time clock and scan keyboard

b $DF08 the last three bytes execute "jp $DF72" when called by $FE6A