The Arithmetic Logic Unit

Below is a circuit of a four (4) input ALU. The input lines are A and B and an output F.  The control lines of the ALU controls what Arithmetic or Logical operation that is to be performed on the inputs. This type of circuit contains more than one microoperation.

S2 S1 S0 Cin    Operation        Function
0  0  0  0      F = A            Transfer A
0  0  0  1      F = A + 1        Increment A
0  0  1  0      F = A + B        Addition
0  0  1  1      F = A + B + Cy   Add with Carry
0  1  0  0      F = A + B'       A plus complement of B
0  1  0  1      F = A + B' + 1   Subtraction
0  1  1  0      F = A - 1        Decrement A
0  1  1  1      F = B            Transfer B
1  0  0  0      F = A & B        AND
1  0  1  0      F = A # B        OR
1  1  0  0      F = A xor B      XOR
1  1  1  0      F = A'           Complement A

If the ALU circuit is mixed with the register circuits, it can now add a significant number of RTLs. Let us try to consider an application wherein the ALU is used with registers.

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