134 Onchip-UIS 4-bit Ripple Carry Adder
134 : Onchip-UIS 4-bit Ripple Carry Adder
- Author: Nestor Matajira
- Description: A structural 4-bit Ripple Carry Adder using half and full adders.
- GitHub repository
- Open in 3D viewer
- Clock: 0 Hz
How it works
This project implements a structural 4-bit Ripple Carry Adder (RCA). It computes the arithmetic sum of two 4-bit unsigned binary numbers ($A$ and $B$) and generates a 5-bit result ($S$).
The hardware architecture uses a modular, multi-stage structure:
- Least Significant Bit (Stage 0): A Half Adder (
sumadormedio) processes $A[0]$ and $B[0]$ to produce the first sum bit $S[0]$ and an initial carry-out $C[0]$. - Intermediate Bits (Stages 1 to 3): Three Full Adders (
sumadorcompleto) sequentially cascade the carry-out from the previous stage ($C_{in}$) with the respective input bits ($A[i]$ and $B[i]$) to compute $S[i]$ and the next $C_{out}$. - Most Significant Bit / Overflow: The final carry-out from the third full adder ($C[3]$) is mapped directly to $S[4]$, representing the final overflow or MSB of the 5-bit result.
Since this design does not include sequential elements (registers or flip-flops), it operates entirely as a combinational block. The global clock (clk), reset (rst_n), and enable (ena) inputs are properly tied off internally to avoid linting warnings during the OpenLane/Yosys synthesis flow.
How to test
To test the operation of the 4-bit adder on the TinyTapeout demoboard:
- Set the Inputs: * Use the first four input switches
ui_in[3:0]to set the 4-bit binary value for operand A.- Use the next four input switches
ui_in[7:4]to set the 4-bit binary value for operand B.
- Use the next four input switches
- Observe the Outputs:
- Read the 5-bit result from the dedicated outputs
uo_out[4:0]. uo_out[0]corresponds to the LSB ($S[0]$), anduo_out[4]corresponds to the final carry-out / MSB ($S[4]$).- The remaining output pins
uo_out[7:5]will stay at a logic low level (0).
- Read the 5-bit result from the dedicated outputs
For example, if you set $A = 0101$ (5 in decimal) on ui_in[3:0] and $B = 0111$ (7 in decimal) on ui_in[7:4], the output pins uo_out[4:0] will display 01100 (12 in decimal).
External hardware
No specialized external hardware are strictly required.
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | A[0] | S[0] | |
| 1 | A[1] | S[1] | |
| 2 | A[2] | S[2] | |
| 3 | A[3] | S[3] | |
| 4 | B[0] | S[4] (Cout) | |
| 5 | B[1] | ||
| 6 | B[2] | ||
| 7 | B[3] |