1. The combinational circuit ARITHMETIC/LOGIC (A/L) performs the following operations depending on the value of the control inputs X, Y, and Z.
X
Y
Z
Result (O)
Cout
0
0
0
B – A
0
0
1
A + B
Carry
0
1
0
A –
Borrow
0
1
1
Φ
Φ
1
0
0
A B
Φ
1
0
1
Φ
Φ
1
1
0
Φ
1
1
1
Φ
Φ
The meanings of symbols are given below:
Symbol
Meaning
+
Arithmetic addition
-
Arithmetic subtraction
4-bit logic AND between corresponding bits of A and B: A3 B3, …, A0 B0.
4-bit logic XOR between corresponding bits of A and B: A3 B3, …, A0 B0.
Φ
Don’t care
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Design and draw this circuit using only the standard components and logic gates given below, paying attention to the maximum number allowed for the first three:
Type
Maximum number allowed
4-bit parallel adders
2
8:1 multiplexer
1
2:4 decoder
1
XOR gates
No restriction
NOT gates
No restriction
OR gates
No restriction
AND gates
No restriction
