1.
(20 pts) Using four full adders, and any combination of AND, OR, and NOT gates you
wish, implement a circuit that implements the following functions for the given inputs; an
example circuit layout is provided. Note that this requires 2scomplement addition.
S0
S1
Cin
Xi
Yi
Operation
0
0
1
A
1
A
0
1
1
A
B'
AB
1
0
1
A
B
A+B+1
1
1
1
A
0
A+1
Xi = Ai
Yi = S0'B' + S1'B
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View Full Document2.
(15 pts) Which of the following circuirts represents a stable latch for some inputs A and B? For
the ones that do, identify the set and reset inputs. For the ones that do not, could you make
them a stable latch by adding NOT gates? How?
Clarification: You learned about the three properties of a latch in lecture. Test various initial
values of Q and verify that each circuit does or does not satisfy these properties.
a) Not a latch  output is a constant regardless of the inputs.
Can be made a latch by adding NOT
gates to the end of the AND gates, making them NAND gates and this circuit a S'R' latch.
b) Not a latch  output is not latched, but follows input A. It is not possible to add NOT gates to
make this a stable latch.
c) Not a latch  output is not latched. Adding a NOT gate to the OR gate to form a NOR gate
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 Spring '08
 
 Computer Architecture, Logic gate, Bitwise operation, Qnext, stable latch

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