Ripple Carry Adder adds 2 n-bit number plus carry input and gives n-bit sum and a carry output. The Main operation of Ripple Carry Adder is it ripple the each carry output to carry input of next single bit addition. Each single bit addition is performed with full Adder operation (A, B, Cin) input and (Sum, Cout) output. The 4-bit Ripple Carry Adder VHDL Code can be Easily Constructed by Port Mapping 4 Full Adder. The following figure represent the 4-bit ripple carry adder.
Ring Counter very similar to shift register. At each clock pulse, data at each flipflop shifted to next flipflop with last output is feed back to the input of first flipflop. Also the first flop is set to ‘1’ at the reset state. so it shift bit ‘1’ to next flipflop for each clock input and repeat the sequence as shown below.