Capabilities of a 4-bit adder IC: Which operation(s) can a standard 4-bit binary adder perform without additional gating logic?

Difficulty: Easy

Correct Answer: addition

Explanation:


Introduction / Context:
A 4-bit adder IC (e.g., 74HC283/74LS283) provides parallel addition of two 4-bit operands with Cin/Cout for cascading. Other arithmetic/logic functions often require external gating or dedicated ALU chips.


Given Data / Assumptions:

  • Device: standard 4-bit adder, not a full ALU.
  • Inputs: A[3:0], B[3:0], Cin; Outputs: S[3:0], Cout.


Concept / Approach:
Plain addition is native. Subtraction can be realized in a system by inverting B and setting Cin=1 (two's-complement technique), but that requires extra inversion hardware; the bare adder alone does not implement subtraction or AND by itself. Therefore, the only operation directly supported by the chip without external gating is addition.


Step-by-Step Solution:

Identify native function from pinout/equations: Sum = A xor B xor Cin.Non-native functions (subtraction/AND) need extra logic.Hence, direct capability = addition only.


Verification / Alternative check:
Datasheets name the part a “binary adder”; subtraction examples always show complemented inputs and Cin=1 using extra gates.


Why Other Options Are Wrong:

Subtraction: Requires complementing B and setting Cin=1.Logical AND: Requires gate logic, not a sum circuit.All of the above / parity: Not provided by a plain adder.


Common Pitfalls:
Assuming ALU capabilities from an adder part number.


Final Answer:
addition

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