Project 2 Basic Logic Circuits

Design and Implementation of SOP and POS circuits

73

Introduction

This project provides further experience with logic circuits. First, you are asked to download a predesigned FPGA configuration (a .bit file) to configure your Boolean with several logic circuits. Your assignment is to interact with the circuits, discover their response to all inputs, deduce their SOP and POS logic equations, and then re-implement them yourself. Next, two circuit requirements are presented as worded descriptions. After capturing the requirements in a truth table, you are asked to design a circuit and checks its performance on the Boolean board. Finally, you are asked to create another circuit using the design methods discussed. Many new terms and concepts are introduced, and these are discussed in the topic documents.

Before you begin, you should:

  • Have the Xilinx Vivado tool installed;
  • Have a Boolean board and know how to program it;
  • Know how to start a Vivado project and construct a basic logic circuit;
  • Understand logic gates and basic logic circuits.

After you’re done, you should:

  • Be comfortable creating new designs in Vivado;
  • Be able to derive logic functions from truth tables;
  • Be able to define SOP and POS logic functions in Verilog;
  • Be able to translate a worded problem description into Verilog.

Background

In this project, you will take some significant steps towards designing your own digital logic circuits. The design process involves many steps that are best learned though doing actual designs, but some fundamental background knowledge will help that process – read the topic documents! If you understand and complete the requirements, you are highly encouraged to complete the challenge as well. And as always, you are invited to go “off script” and complete your own original design extensions as well.

Requirements

1. Configure your Boolean board with a downloaded .bit file, and deduce the logic circuits it contains

Download and decompress the pre-compiled bitstream from the link below. Open the Hardware Manager from Vivado’s main IDE, autoconnect to the Boolean board, select “Program Device”, and select the .bit you just downloaded. The .bit file will configure your Boolean board with four different circuits that use slide switches as inputs and LEDs for outputs. After your board is programmed, you can interact with the circuits, complete the truth tables below to document their behavior, and then deduce their design. Note you do not need to create a project for this task.

Boolean_DL_P2.Zip

Circuit 1

The first circuit uses slide switches SW0 and SW1 as inputs and LD0 as an output. Use the switches to apply all four possible input patterns, and record LD0’s response in the table below (note LD0 will illuminate when the circuit’s output is a ‘1’). When the table is complete, click “Check Result”.

SW1 SW0 LD0
0 0
0 1
1 0
1 1
Circuit 2

The second circuit uses SW1, SW2 and SW3 as inputs, and LD1 as an output. Probe Circuit 2, complete the truth table below, and check your results.

SW3 SW2 SW1 LD1
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1
Circuit 3

The third circuit uses SW4, SW5, SW6, and SW7 as inputs, and LD2 as output. Probe Circuit 3 the same way you did Circuit 1 and 2, complete the truth table below, and check your results.

SW7 SW6 SW5 SW4 LD2
0 0 0 0
0 0 0 1
0 0 1 0
0 0 1 1
0 1 0 0
0 1 0 1
0 1 1 0
0 1 1 1
1 0 0 0
1 0 0 1
1 0 1 0
1 0 1 1
1 1 0 0
1 1 0 1
1 1 1 0
1 1 1 1

Create your own duplicate circuits

After you have completed the truth tables, create your own circuits to implement the same behavior as the three circuits you just probed. Create a new Vivado project, and add a new Verilog source file. Define eight slide switches as inputs, and three LEDs as outputs. Then, based on your truth table results, write three Verilog assignment statements (using SOP logic) to drive the three LEDs exactly as they were driven in the downloaded file. Your competed Verilog module will have three assignment statements; the first one is provided, but you must write the other two. Your Verilog should similar to the code below.


module top (
    input [7:0] sw,
    output [2:0] led
);

assign led[0] = (sw[0] & ~sw[1]) | (~sw[0] & sw[1]);
assign led[1] = // you must write this statement
assign led[2] = // and this one too

endmodule

Create a new constraints file, and connect the Verilog “sw” inputs and “led” outputs to the proper pins on the ZYNQ device. Note: Instead of typing all the entries, you can download the complete Boolean board constraints file at the link below and add it to your project. Note that we selected signal names for all the peripheral devices, so you’ll need to use those same names in your Verilog source file, or change the names in the .xdc file to match whatever names you used in your source file. Boolean .XDC File

When your Verilog and constraints source files are complete, implement the design, program the Boolean board, and check the results. Note: In Vivado, if you execute a process that uses outputs from one or more previous processes, Vivado will automatically check to make sure all previous processes and files are up to date. If any files needed to be updated, Vivado will automatically run any required processes.

2. Try POS Instead

Modify the source file from requirement 1 above by commenting-out the SOP equations, and then create POS equations to drive the LEDs in exactly the same way. The Assessor will check your source file to make sure both the SOP and POS versions are present.

3. Circuit 4

Program your Boolean board with the .bit file you downloaded in requirement 1. That .bit file contains a fourth circuit that uses SW15 – SW12 as inputs, and LD15 - LD12 as an output. SW11 is used as an “enable” signal; that is, this fourth circuit will only work if SW11 is set to a ‘1’. Probe this fourth circuit, create a new Verilog source file that behaves identically, including the SW11 enable signal. Program your Boolean board, and verify it performs identically.

4. Create a New Circuit

An automobile controller receives several sensor inputs from various engine systems. Four of the sensors are: Coolant Temperature (CT) that outputs a “1” when the coolant temperature exceeds 200 degrees; Coolant Low (CL) that outputs a “1” when the coolant level falls below 60% of capacity; Oil Temperature (OT) that outputs a “1” when the oil temperature exceeds 180 degrees, and Oil Low (OL) that outputs a “1” when the oil level falls below 75% capacity.

Design and implement a warning light system that illuminates a blue light whenever any of the following are true:

  • Only the Coolant Level is low
  • Only the Oil Level is low
  • The Oil Temperature is too high and the Oil Level is OK
  • The Coolant Temperature is too high and the Oil Level is too low

And that illuminates a Red light whenever any of the following are true:

  • The Coolant temperature is too high and the Coolant level is too low
  • The Oil Temperature is too high and the Oil Level is too low
  • The Coolant and Oil Temperatures are too high at the same time
  • The Coolant and Oil levels are too low at the same time that the Coolant Temperature is too high and the Oil Temperature is OK.

Note that Blue and Red LEDs are avaialble in the RGD LEDs as individidual signals (check the scheamtic and/or the .xdc file).

Create a Verilog description of a circuit that meets these requirements, and implement the circuit on your Boolean board. Use four slide switches to represent the sensor inputs and use two RGB LEDs for the outputs.

Challenges

1. LED Controller Using Switches

Illuminate an LED only when exactly two of the first four slide switches (SW0, SW1, SW2, SW3) are set to “1”. Illuminate a second LED when exactly three of the next four switches (SW4, SW5, SW6, SW7) are set to “0”.