Name

Computer Organization

EE 3755

Midterm Examination

Wednesday, 30 October 2013, 8:30–9:20 CDT

Alias

Problem 1 (21 pts)

Problem 2 (15 pts)

Problem 3 (25 pts)

Problem 4 (11 pts)

Problem 5 (11 pts)

Problem 6 (11 pts)

Problem 7 (6 pts)

Exam Total (100 pts)

Good Luck!

Problem 1: [21 pts] Consider the module below:

module prob1is(x,y,a,b,c);

input a, b, c; output x, y;

wire a, b, c, x, y; <-- HINT: Declare types for parts b and c.

assign x = !a ^ y;

assign y = b || c;

endmodule

(a) Draw a logic diagram corresponding to the module. Don’t optimize.

Logic diagram of prob1is.

(b) Complete the module below so that it performs the same operation as prob1is but is in explicit structural

form.

Explicit structural form of prob1is. Don’t forget to declare types.

module prob1es(x,y,a,b,c);

input a, b, c; output x, y;

endmodule

(c) Complete the module below so that it performs the same operation as prob1is but is in synthesizable

behavioral form.

Synthesizable behavioral form of prob1is. Don’t forget to declare types.

module prob1sb(x,y,a,b,c);

input a, b, c; output x, y;

endmodule

2

Problem 2: [15 pts] Appearing below is the generic carry lookahead block from the CLA lecture slides.

Remember that it is part of a hierarchical carry lookahead adder.

a0

b0

a1

b1

al-1

bl-1

al-2

bl-2

bl-3

al-3

P

G

l-bit

type-x

adder

CLB-x

cin

ci

s

a b

l bits

s

Value X

(a) The output of one of the AND gates is labeled Value X. Suppose l= 16. Find inputs to the module such

that Value X is 1but all of the other inputs to the generate OR gate are 0.

Value of module inputs needed so that Value X will be 1.

(b) Notice that the module does not have a carry out signal. Add logic to the module above to compute a

carry out signal. (See next part.)

Logic for carry out. Do not add new inputs to the module.

(c) The carry out signal from the previous part isn’t needed in real life. Why not? What if it were used?

Why doesn’t the CLB need a carry out signal?

What would be the problem with using the carry out signal?

3

EE 3755 Midterm: EE 3755 LSU 2013fMidterm

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