8-Bit CLA Adder (2 Cascaded Blocks)

Intermediate

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Specification

01General Operation

8-bit CLA adder built by cascading two 4-bit CLA blocks. The lower block's o_cout drives the upper block's i_cin, producing a carry that *propagates between groups*.

Behaviour (pure combinational):

Lower block: operands i_a(3:0) and i_b(3:0), carry-in i_cin, produces o_sum(3:0) and an intermediate carry.
Upper block: operands i_a(7:4) and i_b(7:4), carry-in = intermediate carry, produces o_sum(7:4) and o_cout.

*Good illustration of the trade-off between strict CLA (O(1) latency, exploding area) and hierarchical CLA.*

02Interface

i_a

Direction: Input
Width: 8 bits
Description: Operand A

i_b

Direction: Input
Width: 8 bits
Description: Operand B

i_cin

Direction: Input
Width: 1 bit
Description: Carry in

o_sum

Direction: Output
Width: 8 bits
Description: Sum

o_cout

Direction: Output
Width: 1 bit
Description: Carry out

← 4-Bit Carry Lookahead Adder

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