CS/COE 447: Spring 2010 Lab 14

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Question 1: Suppose that a lw instruction is executed using the
multi-cycle control shown on the handout (which is from the
multi-cycle execution lecture notes).  State what happens during
each cycle of execution. Your answers should be in terms of A, B,
ALUOut, PC, Memory[...], IR[...], Reg[...], sign-extend, MDR, PC,
etc. as in the lecture notes.  Though you have this answer in your
lecture notes, try to do this just by looking at the Figure, checking
your answers against the lecture notes only if you have to.
















Question 2: Suppose that a lw instruction is executed using the multi-cycle
control shown on the handout.  What are the values of ALUSrcA,
ALUSrcB, IorD and MemToReg during each cycle?  Please fill in the
table below.  (Use X for ``don't care''.)  Please try to do this looking only
at the handout.  You can check your answers against the lecture notes.

                ALUSrcA        ALUSrcB        IorD       MemToReg


Cycle 1



Cycle 2



Cycle 3



Cycle 4



Cycle 5


Question 3: This question is about the components of the multi-cycle
datapath that deal with updates to the PC.

Suppose that the current instruction is an add instruction.  During
which cycle is PCWrite 1?  

During that cycle, what values do the following signals have?

ALUSrcA

ALUSrcB

PCSource

Now suppose the current instruction is a beq, and that the two
registers are equal (so, the branch will be performed).

During cycle 3, what values do the following have?

PCSource

Output of the AND gate at the top left

Output of the OR gate at the top left

Now suppose that the current instruction is a j.

During cycle 3, what values do the following have:

PCWrite

PCSource