Explore Our Topics!

Check out the extensive list of topics we discuss: 

1. Communication Protocols:
   - USB 
   - RS232 
   - Ethernet 
   - AMBA Protocol: APB, AHB and ASB 
   - UART, I2C AND SPI
2. Important concepts in VLSI:
   - Designing a Chip? Here Are the 12 Important Concepts You Need to Know
   - Metastability 
   - Setup time and Hold time
   - Signal Integrity and Crosstalk effect
   - Skews and Slack 
   - Antenna Effect
3. Semiconductor Memories
   
4. Most Frequently Asked Questions in VLSI
5. Transistors:
   - BJT
   - JFET
   - MOSFET
   - CMOS
   - Transmission Gate CMOS
   - Dynamic CMOS
6. Sequential Circuits:
   - Registers
   - Counters
   - Latches
   - Flip Flops
7. FPGA:
   - ASIC vs FPGA
   - FPGA Insights: From Concept to Configuration
   - Full-Custom and Semi-Custom VLSI Designs: Pros, Cons and differences
   - From Theory to Practice: CMOS Logic Circuit Design Rules Made Easy with Examples
8. CMOS Fabrication:
   - CMOS Fabrication
   - Twin-Tub CMOS Technology
9. Combinational Circuits
   - Logic Gates 
   - Boolean Algebra and DeMorgan's Law 
   - Multiplexer (MUX) and Demultiplexer (DEMUX) 
   - Half Adder
   - Full Adder
   - Half Subtractor
   - Full Subtractor
10. Verilog
    - Verilog Datatypes
    - Comments, Numeral Formats and Operators
    - Modules and Ports
    - assign, always and initial keywords
    - Blocking and Non-Blocking Assignments
    - Conditional Statements
    - Looping Statements
    - break and continue Statement
    - Tasks and Functions
    - Parameter and generate
    - Verilog Codes
11. System Verilog: 
    - Disable fork and Wait fork.
    - Fork and Join.
12. Project on Intel Quartus Prime and Modelsim:
    - Vending Machine Controller
13. Xilinx Vivado Projects
    1)VHDL
    - Counters using Testbench code
    - Flip Flops using Testbench code
    - Logic Gates using Testbench code
    - Full Adder using Half Adder and Testbench code
    - Half Adder using Testbench code
    2)Verilog
    - Logic Gates using Testbench code
    - Counters using Testbench code
    - Full Adder using Half Adder and Testbench code
    - Half Adder using Testbench code
14. VLSI Design Flow:
    - Design Flow in VLSI
    - Y chart or Gajski Kuhn Chart
15. Projects on esim:
    - Step-by-Step guide on how to Design and Implement a Full Adder using CMOS and sky130nm PDK
    - Step-by-Step guide on how to Design and Implement a Half Adder using CMOS and sky130nm PDK
    - Step-by-Step guide on how to Design and Implement a 2:1 MUX using CMOS and sky130nm PDK
    - Step-by-Step guide on how to Design and Implement a Mixed-Signal Circuit of 2:1 Multiplexer
16. IoT based project:
    - Arduino
    - Step-by-Step guide on how to Interface Load Cell using Arduino
17. Kmaps:
    - Simplifying Boolean Equations with Karnaugh Maps - Part:2 Implicants, Prime Implicants and Essential Prime Implicants. 
    - Simplifying Boolean Equations with Karnaugh Maps - Part:1 Grouping Rules.
    - Simplifying Boolean Equation with Karnaugh Maps.

Understanding the Full Subtractor: The Complete Subtraction Solution in Digital Electronics

In digital electronics, subtraction is as essential as addition, particularly when dealing with multi-bit numbers. While the Half Subtractor covers basic single-bit subtraction, it falls short when borrow operations come into play. The Full Subtractor is designed to handle these situations, making it a crucial element in advanced digital systems. This blog post will explore the Full Subtractor, its components, operation, and significance.

What is a Full Subtractor?

A Full Subtractor is a combinational circuit that performs the subtraction of two binary bits while accounting for a borrow from a previous stage. Unlike the Half Subtractor, which handles subtraction without borrow consideration, the Full Subtractor manages both the difference and borrow efficiently in multi-bit binary subtraction. It produces two outputs:

• Difference (D)
• Borrow (B_out)

Theoretical Background

Let’s revisit the rules of binary subtraction, adding the case where we borrow from a previous operation:

• 0–0 = 0
• 1–0 = 1
• 1–1 = 0
• 0–1 = 1 (with a borrow of 1)

When performing multi-bit subtraction, the Full Subtractor must also consider an input borrow (B_in) from the previous less significant bit, leading to more complex calculations.

Components of a Full Subtractor

A Full Subtractor involves three binary inputs:

• A: The minuend (the number being subtracted from)
• B: The subtrahend (the number being subtracted)
• B_in: The borrow input from the previous stage

The Full Subtractor employs the following logic gates:

• XOR Gates: To compute the difference
• AND and OR Gates: To compute the borrow output

The logic expressions for the outputs are:

• Difference (D) = A ⊕ B ⊕ B_in
• Borrow out (B_out) = (A’ ANDB) OR ((A ⊕ B)’ AND B_in)

Circuit Diagram

The Full Subtractor circuit is built using the above components, showing how the XOR gates compute the difference and how the AND/OR gates handle the borrow. Here’s a simplified diagram for better understanding:

Truth Table

The Full Subtractor truth table details the results of all possible combinations of the three inputs (A, B, and B_in):

Applications of Full Subtractor

The Full Subtractor is vital in systems requiring multi-bit subtraction, including:

• Arithmetic Logic Units (ALUs): A core component in CPUs for handling multi-bit arithmetic operations.
• Digital Counters: Used in applications that require down-counting, where the Full Subtractor helps manage borrow operations.
• Binary Calculators: Necessary for performing precise binary arithmetic.
• Data Processing Systems: In systems requiring complex binary operations, the Full Subtractor plays a key role in ensuring accurate computations.

Conclusion

The Full Subtractor extends the functionality of the Half Subtractor by accounting for borrow operations, making it indispensable in multi-bit subtraction scenarios. Understanding the Full Subtractor’s logic and applications is essential for advancing in digital circuit design and gaining a deeper insight into how subtraction is handled in various digital systems. As you move toward more complex circuits, mastering the Full Subtractor will provide a strong foundation for future exploration in digital electronics.

Mastering Verilog: Part 9 — Diving into Tasks and Functions

In our ongoing journey to master Verilog, we’ve explored various foundational concepts and advanced features. In this segment, we will focus on two crucial constructs in Verilog programming: Tasks and Functions. Understanding these constructs is essential for creating modular, reusable, and efficient Verilog code.

1. Introduction to Tasks and Functions

Tasks and functions in Verilog are used to encapsulate and reuse code. They help in organizing code into manageable pieces, making it more readable and maintainable. While both tasks and functions serve similar purposes, they have distinct characteristics and use cases.

Often, we encounter repetitive code segments in RTL (Register Transfer Level) that are invoked multiple times. These segments typically do not consume simulation time and often involve complex calculations with varying data values. In such instances, declaring a function to encapsulate the repetitive code can be highly beneficial. A function allows you to process inputs and return a single value, reducing the amount of RTL code you need to write. By calling the function and passing the necessary data for computation, you streamline your code and avoid redundancy.

In contrast, a task is more versatile. Tasks can handle multiple result values, returning them through output or inout arguments. They can include simulation time-consuming elements like ‘@’ or ‘posedge’. While functions do not consume simulation time and return only a single value, tasks may or may not consume simulation time and can return values via output or inout arguments.

Verilog Tasks

A task in Verilog is used to perform a sequence of statements and can include delays and timing control. Tasks are useful for operations that may require multiple statements and potentially involve waiting periods.

Syntax:

task task_name;
// Input and output declarations
input [width-1:0] input_name;
output [width-1:0] output_name;

// Task body
begin
// Task operations
end
endtask

Example:

module TaskExample;
reg [7:0] a, b;
reg [7:0] result;

// Task Definition
task add_two_numbers;
input [7:0] num1, num2;
output [7:0] sum;
begin
#5 sum = num1 + num2; // Perform addition with a delay
end
endtask

initial begin
a = 8'd10;
b = 8'd20;
add_two_numbers(a, b, result); // Call the task
$display(“The result of addition is: %d”, result);
$stop;
end
endmodule

Explanation:
- Task Definition: ‘add_two_numbers’ takes two inputs (‘num1’ and ‘num2’) and provides an output (‘sum’), with a delay of 5 time units before computing the sum.
- Task Call: The task is invoked in the ‘initial’ block to perform the addition.

Key Features of Tasks:
- Can contain delays and timing controls.
- Can have input, output, and inout arguments.
- Can call other tasks.
- May or may not consume simulation time, depending on their contents.

Verilog Functions

A function in Verilog is used for computing a value and returning it. Functions are typically used for simple calculations and must return a single value. They cannot contain delays or timing controls.

Syntax:

function [return_width-1:0] function_name;
input [input_width-1:0] input_name;
// Function body
begin
function_name = expression; // Compute and return value
end
endfunction

Example:

module FunctionExample;
reg [7:0] a, b;
reg [7:0] result;

// Function Definition
function [7:0] add_two_numbers;
input [7:0] num1, num2;
begin
add_two_numbers = num1 + num2; // Compute the sum
end
endfunction

initial begin
a = 8'd15;
b = 8'd25;
result = add_two_numbers(a, b); // Call the function
$display(“The result of addition is: %d”, result);
$stop;
end
endmodule

Explanation:
- Function Definition: ‘add_two_numbers’ takes two inputs and returns their sum.
- Function Call: The function is called in the ‘initial’ block to compute and return the result.

Key Features of Functions:
- Cannot contain delays or timing controls.
- Must return a single value.
- Cannot call tasks.
- Can be used within expressions.

Differences Between Tasks and Functions

Practical Examples

1. Task Example
   Suppose you are designing a complex digital system where you need to perform a sequence of operations with delays. A task can be used to encapsulate this logic and improve code readability.
2. Function Example
   For simple calculations such as computing a checksum or performing bitwise operations, functions can be used within expressions to streamline your code.

Conclusion

Tasks and functions are powerful constructs in Verilog that enable modular, reusable, and efficient coding practices. Tasks are suited for complex operations with timing controls, while functions are ideal for simple computations. By encapsulating repetitive code segments in functions and leveraging tasks for more complex operations, you can enhance code maintainability and efficiency. Mastering these constructs will elevate your ability to design and verify digital systems effectively.

Stay tuned for more insights and advanced topics in our mastering Verilog series!

Mastering Verilog: Part 10 — Understanding parameter and generate Constructs

When working with Verilog, two constructs that can greatly enhance the flexibility and reusability of your code are parameter and generate. These constructs allow you to create more modular and adaptable designs. In this blog, we’ll delve into how these features work and how you can use them effectively in your Verilog code.

Understanding parameter in Verilog

The parameter keyword in Verilog is used to define constants that can be used throughout your module. Parameters allow you to make your design more flexible by allowing you to modify the behavior of your module through parameterization rather than hardcoding values.

• Why Use Parameters?

1. Flexibility: Parameters allow you to easily change values without modifying the core module code.
2. Reusability: You can create more generic and reusable modules by adjusting parameters.
3. Readability: Using parameters can make your code more readable and maintainable.

• How to Define and Use Parameters
  To define a parameter, use the following syntax:

module my_module #(parameter WIDTH = 8, parameter DEPTH = 16) (
 input [WIDTH-1:0] data_in,
 output [WIDTH-1:0] data_out
);
 // Module implementation
endmodule

In this example, WIDTH and DEPTH are parameters with default values of 8 and 16, respectively. You can override these default values when you instantiate the module:

my_module #(.WIDTH(16), .DEPTH(32)) instance1 (
 .data_in(data_in_16),
 .data_out(data_out_16)
);

Example: Parameterized Adder

Objective: Create a simple parameterized adder module that can be configured for different bit-widths.
Code:

module adder #(parameter WIDTH = 8) (
 input [WIDTH-1:0] a,
 input [WIDTH-1:0] b,
 output [WIDTH-1:0] sum,
 output carry_out
);
 assign {carry_out, sum} = a + b;
endmodule

Explanation:

1. parameter WIDTH = 8: This parameter allows you to specify the width of the adder. The default value is 8 bits.
2. input [WIDTH-1:0] a, b: Inputs a and b are vectors with a width specified by the WIDTH parameter.
3. output [WIDTH-1:0] sum: The output sum has the same width as the inputs.
4. assign {carry_out, sum} = a + b: Adds a and b, assigning the sum and carry-out.

Instantiation:

adder #(.WIDTH(4)) adder_4bit (
 .a(4'b1010),
 .b(4'b0101),
 .sum(sum_4bit),
 .carry_out(carry_out_4bit)
);
adder #(.WIDTH(16)) adder_16bit (
 .a(16'h1234),
 .b(16'h5678),
 .sum(sum_16bit),
 .carry_out(carry_out_16bit)
);

This example creates two instances of the adder module: one with a 4-bit width and another with a 16-bit width.

Exploring generate in Verilog

The generate construct is used to create multiple instances of a module or logic based on a parameter or a condition. This can be particularly useful for generating repetitive structures such as arrays of registers or counters.

• Why Use Generate?

1. Code Reduction: Helps reduce repetitive code by allowing you to generate multiple instances or structures with a single block of code.
2. Conditional Instantiation: Allows you to instantiate modules or logic conditionally based on parameters.

• Basic Syntax of Generate
  The generate construct is used in conjunction with genvar and for loops to create multiple instances:

module generate_example #(parameter N = 4) (
    input [N-1:0] in,
    output [N-1:0] out
);
    genvar i;
    generate
        for (i = 0; i < N; i = i + 1) begin : gen_block
            assign out[i] = in[i]; // Example: copying input to output
        end
    endgenerate
endmodule

In this example, the generate block creates N instances of the assign statement. The genvar keyword is used to declare a variable for use in the generate block.

Example: 2-to-1 Multiplexer Array

Objective: Use generate to create multiple instances of a 2-to-1 multiplexer.
Code:

module mux2to1 #(parameter WIDTH = 8) (
    input [WIDTH-1:0] a,
    input [WIDTH-1:0] b,
    input sel,
    output [WIDTH-1:0] y
);
    assign y = sel ? b : a;
endmodule

module top_module #(parameter NUM_MUX = 4) (
    input [NUM_MUX*8-1:0] data_in,
    input [NUM_MUX-1:0] sel,
    output [NUM_MUX*8-1:0] mux_out
);
    genvar i;
    generate
        for (i = 0; i < NUM_MUX; i = i + 1) begin : mux_gen
            mux2to1 #(.WIDTH(8)) mux_instance (
                .a(data_in[i*8 +: 8]),
                .b(data_in[(i+1)*8-1 -: 8]),
                .sel(sel[i]),
                .y(mux_out[i*8 +: 8])
            );
        end
    endgenerate
endmodule

Explanation:

1. mux2to1 Module: A parameterized 2-to-1 multiplexer with a configurable data width.
2. top_module: Uses a generate block to create multiple instances of the mux2to1 module.
3. genvar i: A generate variable used to iterate through the for loop.
   for (i = 0; i < NUM_MUX; i = i + 1): Loop generates NUM_MUX instances of mux2to1.
4. data_in[i*8 +: 8]: Extracts an 8-bit segment from data_in for the a input.
5. mux_out[i*8 +: 8]: Collects the output from each multiplexer instance.

Instantiation:

top_module #(.NUM_MUX(4)) top_instance (
    .data_in({32'hA5A5A5A5, 32'h5A5A5A5A, 32'hFFFF0000, 32'h0000FFFF}),
    .sel(4'b1010),
    .mux_out(mux_out)
);

In this example, top_instance creates a 4-way multiplexer where each instance of mux2to1 is configured to select between pairs of 8-bit inputs.

Conclusion

The parameter and generate constructs in Verilog provide powerful tools for creating flexible, reusable, and efficient designs. Parameters enable you to adjust module behavior and design size without modifying the core module, while the generate construct helps in managing repetitive structures and conditional instantiation.

By mastering these constructs, you can enhance the adaptability and maintainability of your Verilog code, making it more robust and scalable for complex designs.