ELEC 464 : Microcomputer System Design
                          Fall 1995


                    Assignment 6 - Solutions


Question 1

   The design can be simplified by breaking down the problem into a num-
ber of smaller parts. In this case, part of the design is the detection of an I*
 *ACK
cycle and part is detecting interrupt vectors less than 64. These can be com-
bined into something that detects IACK cycles with bad exception vectors.
   The final part of the design can best be approached using a truth table:
      ________________________________________________
      __badiackB_ERRIN__DTACKIN____BERROUT__DTACKOUT___
      _    0    _ 0    _   0     _ _ 0     _    0     _
      _    0    _ 0    _   1     _ _ 0     _    1     _
      _    0    _ 1    _   0     _ _ 1     _    0     _
      _    0    _ 1    _   1     _ _ 1     _    1     _
      _    1    _ 0    _   0     _ _ 0     _    0     _
      _    1    _ 0    _   1     _ _ 1     _    0     _
      _    1    _ 1    _   0     _ _ 1     _    0     _
      _____1______1________1_________1__________0______

   See the attached listings for the CUPL design.

 Question 2

   See the attached program listings for the solution.

 Question 3


  1. The vector at $020, privilege violation, is initialized to $500.

     The vector at $07C, level 7 autovector interrupt, is initialized to $500.

     The vector at $080, trap number 0, is initialized to $600.

  2. The start-up code does not leave the CPU in supervisor mode because
     the S bit in SR is set to 0.

  3. The SSP (A7 when in supervisor mode) has been set to $1000.

  4. the interrupt mask has been set to $7.

  5. The clock signal will cause an interrupt every second, only on the falling
     edge since level 7 interrupts are edge (not level) sensitive.

  6. The level 7 autovector interrupt handler, at $500 will be executed.

  7. The LS byte of what was in the pushed SR (the pushed CCR) will be writ-
     ten to the output port. This byte is composed of the bits corresponding
     to the 000X NZVC flags. This value will be $04 since the bits in the CCR
     were set by MOVE.W #$0704,SR and not changed by either MOVEA or
     BRA LOOP.



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