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Codiode/Problems/Combinational Logic

16-Bit Ripple Carry Adder

HardLogic CircuitBuild

High-speed datapaths require wide arithmetic units where delay accumulates linearly. Connecting multiple adder blocks exposes the fundamental limitation of ripple carry architectures: the carry signal must propagate through every single bit stage before the final sum is valid.

Construct a 16-bit adder using four discrete 4-bit adder blocks. The circuit accepts two 16-bit inputs A and B and produces a 16-bit sum S alongside a 1-bit Cout. The initial carry-in to the lowest block must be tied to logic 0.

| A (hex) | B (hex) | S (hex) | Cout | |-----------|-----------|-----------|--------| | 0x0000 | 0x0000 | 0x0000 | 0 | | 0x00FF | 0x0001 | 0x0100 | 0 | | 0xFFFF | 0x0001 | 0x0000 | 1 |

Constraints

  • Use exactly four 4-bit adder blocks.
  • Tie the initial carry-in of the least significant block to a constant 0.
  • Route the carry-out of each block to the carry-in of the adjacent more significant block.
  • Do not use a single 16-bit behavioral addition block.

Topics

arithmeticcritical-pathdatapath

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