Fast carry propagation circuit for 5211-coded decimal arithmetic - performs addition and fast propagation of decimal carry signal with minimal gate count

摘要

The circuit takes a 5211-encoded decimal digit (A) and an arithmetic carry signal (x) as inputs, and produces a 5211-encoded decimal digit (B) and a carry output (y). Fast carry propagation is ensured by the direct connection of all input signals to a 4-input AND gate (3), which produces the carry output. The total gate count is increased to 23 if only 2-input gates are used. ADVANTAGE - Can be realised with gate count of eighteen. Performs fast 9+1 carry addition, without additional delay when carry must be propagated to output.