EE264 Introduction to Digital Design Project-2

1. Objective:

The main objective of this project is to design and simulate the One-Bit Full-Adder Using VHDL (hardware description language); which helps us to get familiar with the designing, coding and simulation process using VHDL.

2. Discussion

2.1 One-Bit-Full-Adder

One Bit Full Adder is an important/essential component of design for all types of processor including digital processor, Arm processor, micro processer, etc. A one-bit full adder, used in this simulation process is a device that uses three binary inputs A, B, C-in and two binary outputs sum(s) and c-out. The simulation process was achieved using the VHDL (hardware description language). There are several ways to implement a 1 bit full header. This simulation uses the following implementation to achieve the expected specification for sum(s) and c-out.

∑ (s )=' A ' XOR ' B' XOR'C ¿ ' . (1)

cout=( ' A '∧' B ' )+¿. (2)

The design will use the Boolean function from equation 1 and 2 and produces the final truth table that will similar to the following table:-

Where A, B and ' C ¿ are input and S (sum) and cout are

output and carry out representation respectively.

Figure 1. 1 Bit Full Adder Truth Table

The summation is symbolically listed below along with the block diagram in figure 2. To meet the specification, the design must use Boolean operation described in the equation 1 and 2. The visual representation for inputs and outputs are represented in block diagram in figure-2

A + B c¿

Scout

3. Schematics:

Figure 2.Symbolic addition of a column of three bits and Block diagram

4. Waveform:

Following figure:-3 is a waveform for One-Bit Full-Adder, generated using VHDL program. The waveform is zoomed to 100ns, showing both inputs and outputs.

Figure:-3 , Simulated waveform

The testing results was tested by moving the yellow line into time axis, the results is shown in Table 1

Time (ns) A B Cin Cout

S(Sum)

5 0 0 0 0 015 1 0 0 0 125 0 1 0 0 135 1 1 0 1 045 0 0 1 0 155 1 0 1 1 065 0 1 1 1 075 1 1 1 1 1

Table 1. Testing Result

The testing result was compared with truth table of the 1bit full adder. The result has been verified that the testing results are same as the results from the original truth table from figure 1.

5. Project Summery

LUT=

Slice =

IO utilization in percentage=

6. Self-Evaluation: Overall project was very informative and fun to complete. We were somewhat familiar with the VHDL software from project-1, but then also we faced difficulties to write the VHDL code. We watched some tutorial video on VHDL, deed some research, and review the note from class, about conversion of project one code to solve our problems. At the end, we end up figuring out the procedure and modify the code from project one and make it functional.

7. Code

Following figure:-4, is a VHDL source code for this exercise and figure:-5 , is a code for test bench.

Figure 4.Source File Code

Figure 5.Simulation testbench Code