An ALU performs arithmetic and logical operation and is a fundamental building b

Question

An ALU performs arithmetic and logical operation and is a fundamental building block of the CPU (central processing unitof a computer. We wish to design a 4-bit ALU with the existing MSI components. The ALU has 10 inputs A3, A2, Ai, Ao: 4-bit operand A. A is in 2's complement format and A3 is MSB. B3, B2, B1, Bo: 4-bit operand B. B is in 2's complement format and B3 is MSB. Si, So: 2-bit control signal specifying the desired operation. and 4 outputs: F3, F2, F1, Fo: it result F. Fis in 2's complement format and F3 is MSB. The functional table of this circuit is ISSO F F F Fo description 000 A3A2A A0+BaB2B Bo addition A3A2AIAO-BaB2B Bo subtraction 10 A B3, A2 B2, Al Bun, A0. Bo bit-wise AND operation 11 A3 or B3, A2 or B2, A1 or B1, Ao or Bo bit-wise OR operation

Explanation / Answer

Question a) Is it a good idea to use the truth-table method to design the ALU circuit.

Answer: I dont think its always the good method to use truth-table in design the circuit. The reasons for that are given below:

1) Truth-table method is a lengthy procedure.
2) Truth-table method is very conventional and its the old method.
3) In place of truth-table, we can use the iterative method of cascading the standard funtion. With this we can a very simple implementation

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