The Circuit Board - Your Ultimate Guide to Electronics and VLSI Design

Hello, I'm Radha Kulkarni, an electronics engineer and a passionate blogger focused on VLSI and electronics concepts. I share my knowledge of VLSI and electronics concepts through informative and engaging blogs. My content covers a range of topics, including the latest trends, best practices, and insights into the industry. As someone passionate about my work, I enjoy connecting with others who share my interests and look forward to building a community around VLSI and electronics. Thank you!

Showing posts with label xilinx. Show all posts

November 20, 2024

Explore Our Topics!

Check out the extensive list of topics we discuss:

Communication Protocols:
- USB
- RS232
- Ethernet
- AMBA Protocol: APB, AHB and ASB
- UART, I2C AND SPI
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
Semiconductor Memories
Most Frequently Asked Questions in VLSI
Transistors:
- BJT
- JFET
- MOSFET
- CMOS
- Transmission Gate CMOS
- Dynamic CMOS
Sequential Circuits:
- Registers
- Counters
- Latches
- Flip Flops
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
CMOS Fabrication:
- CMOS Fabrication
- Twin-Tub CMOS Technology
Combinational Circuits
- Logic Gates
- Boolean Algebra and DeMorgan's Law
- Multiplexer (MUX) and Demultiplexer (DEMUX)
- Half Adder
- Full Adder
- Half Subtractor
- Full Subtractor
- Encoders
- Decoder
Analog Electronics
- OPAMP
- Inverting and Non-inverting Amplifiers
- Characteristics of OPAMP
- OPAMP Application: Adder, Subtractor, Differentiator, and More!
- Filters
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
System Verilog:
- Disable fork and Wait fork.
- Fork and Join.
Project on Intel Quartus Prime and Modelsim:
- Vending Machine Controller
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
VLSI Design Flow:
- Design Flow in VLSI
- Y chart or Gajski Kuhn Chart
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
IoT based project:
- Arduino
- Step-by-Step guide on how to Interface Load Cell using Arduino
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.

November 24, 2023

Mastering Verilog: Part 5 - Understanding Blocking and Non Blocking Statements

Procedural Statements in Verilog, such as blocking and non-blocking assignments, are categorized as elements of procedural blocks, such as ‘always’ and ‘initial.’
These statements play a crucial role in updating variables, and once a value is assigned, it remains unchanged until another procedural assignment modifies it. This stands in contrast to continuous assignments, where the value of a variable changes continuously.
In procedural assignments, the order of signal assignments and the flow of execution are explicitly determined, providing control over the sequencing of operations within the design.
Procedural blocks in Verilog primarily fall into two categories:

always Blocks:
Usage: Utilized to describe both combinational and sequential logics, triggered by events such as a clock edge (posedge or negedge).
Example:
always @(posedge clk) begin
// Sequential or combinational logic here
end
initial Blocks:
Usage: Employed to specify initial conditions or setup during simulation, executing once at the beginning.
Example:
initial begin
// Initialization logic here
end

Now let us see how these procedural statements work.

1] Blocking assignments:

Syntax:
Specified using the ‘=’ operator.
Execution Flow:
Statements are executed sequentially in the order specified within the procedural block.
The execution of subsequent statements is blocked until the current assignment is completed.
Scope:
Blocking assignments within one procedural block do not impact the execution of statements in other procedural blocks.
Example:
Now let us consider below example to understand how blocking statements work. Below is not the complete verilog code but a module to understand the concept.

integer x,y,z;
initial
begin
x = 20;
y = 15;
z = 30;
x = y + z;
y = x + 10;
z = x — y;
end

Now the output for above logic will be as follows:

initially, x=20,y=15,z=30
x becomes 45
y becomes 55
z becomes -10

Initial Values:
Initially, the values of x, y, and z are set to 20, 15, and 30, respectively.
Execution Steps:
After the execution of the first statement (x = y + z), the value of x becomes 45.
The second statement (y = x + 10) utilizes the updated value of x (now 45), resulting in y becoming 55.
Finally, the third statement (z = x — y) uses the updated values of x (45) and y (55), causing z to become -10.

Provided below is the Verilog code for the logic mentioned above. Experiment with its implementation in simulation software to observe the output.

module blocking_assignment;
reg [31:0] x, y, z;
initial begin
x = 20;
y = 15;
z = 30;
// Blocking assignments
x = y + z; // x is assigned the value of y + z (15 + 30 = 45)
y = x + 10; // y is assigned the value of x + 10 (45 + 10 = 55)
z = x — y; // z is assigned the value of x — y (45–55 = -10)
// Displaying the values after the assignments
$display(“x = %0d, y = %0d, z = %0d”, x, y, z);
end
endmodule

Now let us consider the same example but with delays:

integer x,y,z;
initial
begin
x = 20;
y = 15;
z = 30;
x = y + z;
#5 y = x + 10;
#10 z = x — y;
end

Now the output for above logic will be as follows:

initially, x=20,y=15,z=30
x becomes 45
y becomes 55
z becomes -10

Initial Values:
Initially, the values of x, y, and z are set to 20, 15, and 30, respectively.
Execution Steps:
After the execution of the first statement (x = y + z), the value of x becomes 45.
At time 0, the second statement (#5 y = x + 10) is scheduled to occur at time 5.
However, this scheduling doesn’t affect the immediate execution of the next statement.
At time 0, the third statement (#10 z = x — y) is scheduled to occur at time 10 + 5 = 15.
This means that the actual execution of the third statement occurs at time 15.
So, in the scenario with delays, the execution of the third statement (z = x — y) occurs at time 15, not immediately after the second statement. Therefore, the value of z becomes -10 at time 15.

2] Non Blocking Assignment:

Syntax:
Specified using the ‘<=’ operator.
Key Characteristics:
Non-blocking assignments allow concurrent execution of statements within the same procedural block and do not block the execution of the next statement.
Particularly suitable for sequential logic implementation in Verilog, commonly used to model flip-flops and other sequential elements in digital circuits.
Sequential Logic Implementation:
Non-blocking assignments help avoid race conditions in sequential logic design.
When multiple signals are updated within the same clocked always block, non-blocking assignments ensure that all updates occur simultaneously at the next clock edge.
Example:
Let’s consider the same example used for blocking statements to illustrate how non-blocking statements work:

integer x, y, z;
initial begin
x = 20;
y = 15;
z = 30;
x <= #10 y + z;
y <= #10 x + 10;
z <= #10 x — y;
end

Output Explanation:
Initially, the values of x, y, and z are set to 20, 15, and 30.
After the execution of the statements at time 10 (due to delays), the values become:
x becomes 45
y becomes 30
z becomes -5
Initially, the values of x, y, and z are set to 20, 15, and 30, respectively.
According to the given delay (#10), all statements within the initial block will execute at time 10 and will consider the initially defined values for calculation.

In conclusion, the significance of blocking and non-blocking assignments in Verilog coding cannot be overstated. These elements serve as the foundation for precise and effective digital circuit design, offering control over sequential and concurrent execution. As you venture further into the intricacies of Verilog, remember that mastering the art of assignments empowers you to create resilient and optimized digital systems. Happy coding!

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November 2, 2023

Verilog - NOT Gate

not_gate.v

module and_gate(a,y);
input a;
output y;

not(y,a);
endmodule

tb_not_gate.v

module tb_not_gate;
reg a;
wire y;

not_gate UUT (.a(a), .y(y));

initial begin
$display(“Testing NOT gate”);

a = 0;
#10;
$display(“Input_A = %b, Output = %b”, a,y);

a = 1;
#10;
$display(“Input_A = %b, Output = %b”, a,y);

$finish;
end
endmodule

The output waveform for not gate will be as follows:

Verilog - XNOR Gate

xnor_gate.v

module xnor_gate(a,b,y);
input a;
input b;
output y;

xnor(y,a,b);
endmodule

tb_xnor_gate.v

module tb_xnor_gate;
reg a;
reg b;
wire y;

xnor_gate UUT (.a(a), .b(b), .y(y));

initial begin
$display(“Testing XNOR gate”);

a = 0; b=0;
#10;
$display(“Input_A = %b, Input_B = %b, Output = %b”, a,b,y);

a = 0; b=1;
#10;
$display(“Input_A = %b, Input_B = %b, Output = %b”, a,b,y);

a = 1; b=0;
#10;
$display(“Input_A = %b, Input_B = %b, Output = %b”, a,b,y);

a = 1; b=1;
#10;
$display(“Input_A = %b, Input_B = %b, Output = %b”, a,b,y);

$finish;
end
endmodule

The output waveform for xnor gate will be as follows:

Verilog - XOR Gate

xor_gate.v

module xor_gate(a,b,y);
input a;
input b;
output y;

xor(y,a,b);
endmodule

tb_xor_gate.v

module tb_xor_gate;
reg a;
reg b;
wire y;

xor_gate UUT (.a(a), .b(b), .y(y));

initial begin
$display(“Testing XOR gate”);

a = 0; b=0;
#10;
$display(“Input_A = %b, Input_B = %b, Output = %b”, a,b,y);

$finish;
end
endmodule

The output waveform for xor gate will be as follows:

Verilog - NOR Gate

nor_gate.v

module nor_gate(a,b,y);
input a;
input b;
output y;

nor(y,a,b);
endmodule

tb_nor_gate.v

module tb_nor_gate;
reg a;
reg b;
wire y;

nor_gate UUT (.a(a), .b(b), .y(y));

initial begin
$display(“Testing NOR gate”);

a = 0; b=0;
#10;
$display(“Input_A = %b, Input_B = %b, Output = %b”, a,b,y);

$finish;
end
endmodule

The output waveform for nor gate will be as follows:

Verilog - NAND Gate

nand_gate.v

module nand_gate(a,b,y);
input a;
input b;
output y;

nand(y,a,b);
endmodule

tb_nand_gate.v

module tb_nand_gate;
reg a;
reg b;
wire y;

nand_gate UUT (.a(a), .b(b), .y(y));

initial begin
$display("Testing NAND gate");

a = 0; b=0;
#10;
$display("Input_A = %b, Input_B = %b, Output = %b", a,b,y);

a = 0; b=1;
#10;
$display("Input_A = %b, Input_B = %b, Output = %b", a,b,y);

a = 1; b=0;
#10;
$display("Input_A = %b, Input_B = %b, Output = %b", a,b,y);

a = 1; b=1;
#10;
$display("Input_A = %b, Input_B = %b, Output = %b", a,b,y);

$finish;
end
endmodule

The output waveform for nand gate will be as follows:

Verilog - Or Gate

or_gate.v

module or_gate(a,b,y);
input a;
input b;
output y;

or(y,a,b);
endmodule

tb_or_gate.v

module tb_or_gate;
reg a;
reg b;
wire y;

or_gate UUT (.a(a), .b(b), .y(y));

initial begin
$display(“Testing OR gate”);

a = 0; b=0;
#10;
$display(“Input_A = %b, Input_B = %b, Output = %b”, a,b,y);

$finish;
end
endmodule

The output waveform for or gate will be as follows:

Step-by-step guide on how to design and implement Logic Gates with testbench code on Xilinx Vivado design tool using Verilog HDL.

In this project, we will see how to implement all logic gates with verilog testbench code on Xilinx Vivado design tool. Below diagram shows all logic gates along with there truth tables, symbol and Boolean equation.

Now let us see how we will implement these gates using Xilinx Vivado design tool.

Step 1: Click on New Project -> Next

Step 2: Enter Project Name and Select appropriate Project Location -> Next

Step 3: Select RTL Project -> Next

Step 4: Click on Create File and create file with file name and_gate -> Next

Step 5: We will not add the Constraint file So click on Next

Step 6: For Default Part click on Next as we are not using any development Board

Step 7: Check the New Project Summary and click on Finish.

Step 8: Now you will be prompted with the Define module page but we will create the complete code from scratch so click on cancel and Yes

Step 9: Now on the Home Page click on Sources -> Design Sources -> Non-module Files

Step 10: Enter the below codes in the “and_gate.v” files.

and_gate.v

module and_gate(a,b,y);
input a;
input b;
output y;

and(y,a,b);
endmodule

Step 11: Now to write the testbench code for and gate right click on Design Sources -> Add Sources -> Add or create design sources -> Create File -> Add File name as tb_and_gate -> Finish -> Ok -> Yes

Step 12: Now open the testbench file and enter the below testbench code

module tb_and_gate;
reg a;
reg b;
wire y;

and_gate UUT (.a(a), .b(b), .y(y));

initial begin
$display(“Testing AND gate”);

a = 0; b=0;
#10;
$display(“Input_A = %b, Input_B = %b, Output = %b”, a,b,y);

$finish;
end
endmodule

Here, in testbench code we do not define values in entity hence we have kept it empty. Then in architecture we have copied the components of and_gate and defined signals for connecting the ports of and gate. Inside the process statement we write all 4 test cases from truth table and define the delay as 100ns.