UPC EETAC Bachelor's Degree in Telecommunications Systems and in Network Engineering EEL

 

Adder_1bit: structural single-file VHDL, plan A

P3

Structural design of a 1-bit full adder circuit  (Plan A)

1. Specifications Planning Developing Testing Report Prototype

Design a 1-bit adder using structural equations.


Adder    		Adder

Fig. 1. Symbol and truth table of a 1-bit adder circuit. It is also called full adder.

This in Fig. 2 is a simple sketch that represents the truth table in time. The idea of applying input vectors that can be any binary combination.

 

Fig. 2. Timing diagram where all the inputs are applied sequentially and hence, the output is predicted accordingly to the truth table.

 

Specifications 2. Planning Developing Testing Report Prototype

The VHDL file will be named Adder_1bit.vhd, the same name given to the entity. The project name is Adder_1bit_prj.

The block's architecture can be derived from equations (plan A). Thus, consider a broad view of the problem. This is a list of planning examples, and the list index is giving you an idea on how to name the corrsponding project folder:

Plan A ) Structural using equations (flat, single file project):

A1_M.- Truth table represented as a product of maxterms (canonical circuit)

A2_m.- Truth table represented as a sum of minterms (canonical circuit).

A3_SoP.- Simplified equations using Minilog.exe: SoP.

A4_PoS.- Simplified equations using Minilog.exe: PoS.

A5_NOR.- It is also possible to modify any of previous equations in order to use only-NOR gates.

A6_NAND.- It is also possible to modify any of previous equations in order to use only-NAND gates.

A7.- Any other equation. For instance, this is an implementation realising that XOR gates can be used to replace some AND and OR gates, which makes a simpler circuit. And rec. is a video recording of the project.

 

Specifications Planning 3. Developing Testing Report Prototype

This is the translation to VHDL Adder_1bit.vhd of the 7th structural description from above. The project location is

L:\CSD\P3\Adder_1bit_A7\(files)

Run a EDA project to synthesise the circuit. Fig. 3 shows an example of RTL schematic.

   RTL strcutural

Fig. 3. Example RTL when the project is developed  using some sort of equations like the ones written in plan A7.

 

Specifications Planning Developing 4. Testing Report Prototype

An example test bench Adder_1bit_tb.vhd. Run the VHDL simulation EDA tool to obtain and discuss the timing diagram.  Remember that from the testing point of view, even if you have designed the Adder_1bit using several plans, you can use all the time the same testbench.

   tEST

Fig. 4. Example testbench showing results

 

Specifications Planning Developing Testing 5. Report Prototype

Follow this rubric for writing reports.

 

Specifications Planning Developing Testing Report 6. Prototype

We can use the DE10-Lite board to implement this project, as shown in Lab 1.2. Study the user manual and generate a HEX_7seg_decoder_top schematic to assign input and output pins.