7-Segment Display in VHDL Programming Language

Introduction to 7-Segment Display in VHDL Programming Language

Hello, and welcome to this blog post on how to work with a 7-Segment Display in VHDL Pr

ogramming Language! Whether you are new to VHDL or just looking to refresh your knowledge, you’ve come to the right place. In this post, I will guide you through the basics of using a 7-segment display in your VHDL projects. You’ll learn how to design and simulate the necessary code to drive the display and show numbers from 0 to 9. By the end of this post, you’ll be ready to create your own digital systems with 7-segment displays. Let’s get started!

What is 7-Segment Display in VHDL Programming Language?

A 7-segment display is an electronic device that features seven individual segments arranged in the shape of the number 8. Users can individually turn these segments on or off to display decimal digits (0-9) or certain alphabetic characters. This display commonly appears in digital clocks, calculators, and other electronic devices that show numeric information.

In VHDL (VHSIC Hardware Description Language), you control a 7-segment display through digital logic by sending the appropriate signals to the individual segments to represent a specific number or character. Designers often use VHDL to implement the control logic for these displays in hardware systems like FPGAs or ASICs.

Name	Location
A	Top Middle
B	Top Right
C	Bottom Right
D	Bottom Middle
E	Bottom Left
F	Top Left
G	Middle
DP	Decimal Point

Components of a 7-Segment Display

The 7-segment display consists of the following key components:

1. Seven Segments (labeled A to G):

Each segment contains an individual light-emitting diode (LED) or liquid crystal that you can turn on or off. These segments arrange themselves to form the shape of the numbers.

• The segments are usually labeled as: A, B, C, D, E, F, and G, forming the number “8” when all segments are turned on.

2. Common Pin:

The display can use either a common anode or common cathode configuration, connecting all the anodes or cathodes of the LEDs to a common pin.

• Common Anode: In this configuration, you connect the anode (positive terminal) of all the segments to a common point, and you turn on the segments by pulling their cathodes low.
• Common Cathode: In this configuration, you connect the cathode (negative terminal) of all segments to a common point, and you turn on the segments by applying a high signal to their anodes.

How a 7-Segment Display Works

• Displaying a Digit: To display a particular digit, the appropriate combination of segments needs to be turned on.
• For example:
  • To display the digit 0, segments A, B, C, D, E, and F are turned on, while segment G remains off.
  • To display the digit 1, only segments B and C are turned on.
  • For 8, all segments (A to G) are turned on.

• Binary Input to 7-Segment Display: The number to be displayed is typically provided in binary or BCD (Binary Coded Decimal) form, which is then decoded to drive the correct segments.

7-Segment Display in VHDL

In VHDL, the control logic for a 7-segment display is written by designing a decoder circuit. This decoder receives a binary input (representing numbers 0-9) and generates the correct signals for the corresponding segments.

Steps to Implement 7-Segment Display in VHDL:

• Define Input and Output Signals:
  • Input: A 4-bit binary number (usually representing a decimal number 0-9).
  • Output: Seven individual control lines corresponding to the seven segments (A to G).

• Create a Decoder Logic:
  • The decoder is responsible for converting the input binary value into the correct combination of segment control signals. For instance:
    • Input “0000” (binary for 0) will light up segments A, B, C, D, E, F (to form the number 0).
    • Input “0001” (binary for 1) will light up segments B and C.

• Write the VHDL Code:
  • A process block in VHDL is used to implement the decoding logic. Depending on the input, different segments will be turned on or off.

Example of basic VHDL code for a 7-segment display:

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity seven_segment is
    Port ( binary_input : in STD_LOGIC_VECTOR (3 downto 0);
           segments : out STD_LOGIC_VECTOR (6 downto 0));
end seven_segment;

architecture Behavioral of seven_segment is
begin
    process(binary_input)
    begin
        case binary_input is
            when "0000" => segments <= "1111110"; -- 0
            when "0001" => segments <= "0110000"; -- 1
            when "0010" => segments <= "1101101"; -- 2
            when "0011" => segments <= "1111001"; -- 3
            when "0100" => segments <= "0110011"; -- 4
            when "0101" => segments <= "1011011"; -- 5
            when "0110" => segments <= "1011111"; -- 6
            when "0111" => segments <= "1110000"; -- 7
            when "1000" => segments <= "1111111"; -- 8
            when "1001" => segments <= "1111011"; -- 9
            when others => segments <= "0000000"; -- Blank
        end case;
    end process;
end Behavioral;

In this code:

• binary_input is the 4-bit input representing the binary value of the decimal digit.
• segments is the 7-bit output that controls the individual segments of the display (where each bit corresponds to a segment: A to G).

Common Applications

• Digital Clocks: Used to display time by showing numbers 0 to 9.
• Counters and Timers: Display numbers counting up or down, such as in stopwatches or event counters.
• Calculators: To show numeric input and results.

Challenges in VHDL Implementation

• Timing Considerations: When using a multiplexed display, ensuring that the display refreshes fast enough to avoid flicker can be tricky, especially when dealing with multiple digits.
• Power Consumption: In larger designs with many digits, controlling the power consumption while keeping all the digits visible requires careful design of the multiplexing logic.

Why do we need 7-Segment Display in VHDL Programming Language?

The 7-segment display ranks among the most commonly used devices for visually representing numeric information in electronic systems. Implementing a 7-segment display in VHDL (VHSIC Hardware Description Language) proves crucial for several reasons:

1. Simple Visual Representation of Data

• Human-readable Output: A 7-segment display enables humans to easily understand binary data processed within digital systems. The display translates complex binary values into familiar numerical digits, like those used in clocks, counters, and calculators.
• Numeric Feedback: When working with FPGA designs or digital circuits, using a 7-segment display gives immediate numeric feedback, helping users verify outputs like counters, timers, and other number-based logic.

2. Ease of Integration in Digital Systems

• Direct Hardware Interface: You can easily integrate the 7-segment display into digital systems using VHDL. The binary inputs processed by FPGA or digital logic directly map to the display segments, making it an efficient output device for visual representation.
• Compact and Simple Design: Unlike more complex display types (e.g., LCD or OLED), 7-segment displays have a simpler architecture, requiring fewer control signals, which reduces the need for complex interfacing circuits.

3. Educational Value

• Understanding Binary to Decimal Conversion: In VHDL, working with a 7-segment display is an excellent way to teach students or beginners how to convert binary data to decimal representations. This includes designing binary-to-7-segment decoders, understanding segment control, and practicing combinational logic design.
• Learning Digital System Design: Implementing a 7-segment display in VHDL helps learners build fundamental skills in hardware description languages (HDLs), such as binary input/output, decoding logic, and signal driving.

4. Real-time Display in Embedded Systems

• Counters and Timers: You often use 7-segment displays in counters and timers, such as digital stopwatches and timers in industrial systems. VHDL can control the display of numbers in real-time, making it useful in scenarios that require time- or count-based feedback.
• Digital Readouts: Many embedded applications, such as temperature monitoring systems, voltage measurement tools, and event counters, use 7-segment displays to show numeric values in real-time.

5. Practical Applications in FPGA Projects

• Cost-effective Display Solution: 7-segment displays provide a low-cost, simple solution for visual output in FPGA-based projects. When designing small-scale systems like digital clocks, calculators, or simple counting devices, the 7-segment display serves as an efficient and practical output method.
• Multiplexing for Multiple Digits: Using a 7-segment display with multiple digits is common in VHDL designs. By multiplexing the displays, you can represent large numeric values across several digits without significantly increasing the complexity of the design.

6. Widely Used in Real-world Systems

• Commercial and Industrial Use: 7-segment displays are still widely used in commercial products such as gas pumps, microwave ovens, and vending machines. VHDL is ideal for designing the control logic for these devices, providing robust hardware-level implementations that are efficient and reliable.
• Low Power Consumption: For battery-operated or low-power devices, 7-segment displays offer a more energy-efficient alternative to other display technologies. VHDL-based designs can control the display’s power consumption by selectively turning off unused segments or multiplexing displays.

7. Simplicity in FPGA or ASIC Designs

• Basic Display Mechanism: Compared to more complex display units like graphical LCDs or OLEDs, the 7-segment display is easier to control and requires less memory and processing power, making it an attractive choice for FPGA or ASIC designs.
• Resource-efficient Design: Implementing a 7-segment display in VHDL requires fewer resources compared to more sophisticated display units. This makes it suitable for applications where hardware resources, such as logic elements or memory, are limited.

Example of 7-Segment Display in VHDL Programming Language

A 7-segment display is a common output device used to visually represent decimal digits using an array of 7 LEDs (segments) arranged in a figure-eight pattern. Each segment can be turned on or off to display the numbers 0 through 9 and some letters. In this example, we will walk through the VHDL implementation of a simple 7-segment display driver that takes a 4-bit binary input (representing numbers 0-9) and controls the segments accordingly.

Components of the 7-Segment Display

• Segments: The display consists of seven segments, typically labeled as follows:
  • A (top)
  • B (top right)
  • C (bottom right)
  • D (bottom)
  • E (bottom left)
  • F (top left)
  • G (middle)

• Common Cathode vs. Common Anode: In a common cathode configuration, the cathodes of all the segments are connected together, and each segment is lit by applying a high signal (logic 1) to its anode. In a common anode configuration, the anodes are connected together, and a low signal (logic 0) turns on the segments.

For this example, we will assume a common cathode display.

VHDL Code for 7-Segment Display

Here’s a detailed VHDL example for a 7-segment display driver that accepts a 4-bit binary input and drives the display accordingly:

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity seven_segment_display is
    Port ( binary_input : in STD_LOGIC_VECTOR (3 downto 0); -- 4-bit binary input (0-9)
           segments : out STD_LOGIC_VECTOR (6 downto 0) -- Output to segments A to G
         );
end seven_segment_display;

architecture Behavioral of seven_segment_display is
begin
    process(binary_input)
    begin
        case binary_input is
            when "0000" => segments <= "1111110"; -- 0: A, B, C, D, E, F ON
            when "0001" => segments <= "0110000"; -- 1: B, C ON
            when "0010" => segments <= "1101101"; -- 2: A, B, D, E, G ON
            when "0011" => segments <= "1111001"; -- 3: A, B, C, D, G ON
            when "0100" => segments <= "0110011"; -- 4: B, C, F, G ON
            when "0101" => segments <= "1011011"; -- 5: A, C, D, F, G ON
            when "0110" => segments <= "1011111"; -- 6: A, C, D, E, F, G ON
            when "0111" => segments <= "1110000"; -- 7: A, B, C ON
            when "1000" => segments <= "1111111"; -- 8: A, B, C, D, E, F, G ON
            when "1001" => segments <= "1111011"; -- 9: A, B, C, D, F, G ON
            when others => segments <= "0000000"; -- Blank for invalid inputs
        end case;
    end process;
end Behavioral;

Explanation of the Code

1. Library Declaration:

The IEEE library is included, which provides standard data types and functions for VHDL programming.

2. Entity Declaration:

The entity named seven_segment_display defines the interface for the 7-segment display driver.

• Inputs: binary_input: A 4-bit vector representing the binary number (0-9).
• Outputs: segments: A 7-bit vector where each bit corresponds to a segment of the display (A to G).

3. Architecture Declaration:

The Behavioral architecture describes how the output segments are driven based on the input.

4. Process Block:

• A process block is used to respond to changes in the binary_input. Inside the process:
• The case statement evaluates the value of binary_input and assigns the appropriate segment control signals to segments.
• Each case corresponds to a digit from 0 to 9. The binary input directly maps to segments:
  • For example, when binary_input is "0000" (which represents 0), the output segments is set to "1111110" indicating that segments A, B, C, D, E, and F are turned on to display the number 0.
  • The when others clause is included to handle invalid inputs by turning off all segments.

Simulation and Testing

To verify that the VHDL design works correctly, you can simulate the code using a VHDL simulator such as ModelSim, Vivado, or GHDL. You would create a testbench to apply various values to binary_input and observe the output on segments.

Example Testbench:

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity tb_seven_segment_display is
end tb_seven_segment_display;

architecture behavior of tb_seven_segment_display is

    signal binary_input : STD_LOGIC_VECTOR(3 downto 0);
    signal segments : STD_LOGIC_VECTOR(6 downto 0);

    component seven_segment_display
        Port ( binary_input : in STD_LOGIC_VECTOR (3 downto 0);
               segments : out STD_LOGIC_VECTOR (6 downto 0));
    end component;

begin

    uut: seven_segment_display
        Port map ( binary_input => binary_input,
                   segments => segments);

    process
    begin
        -- Test all inputs from 0 to 9
        for i in 0 to 9 loop
            binary_input <= std_logic_vector(to_unsigned(i, 4));
            wait for 10 ns; -- Wait for output to settle
        end loop;

        -- Test invalid input
        binary_input <= "1010"; -- Invalid input
        wait for 10 ns;

        wait; -- End simulation
    end process;

end behavior;

Advantages of 7-Segment Display in VHDL Programming Language

Using a 7-segment display in VHDL programming has several advantages that make it a popular choice for displaying numerical and some alphanumeric information in digital circuits. Here are the key benefits:

1. Simplicity in Design

A 7-segment display is straightforward to interface with microcontrollers and FPGAs, requiring only a few output lines. This simplicity allows designers to create circuits with minimal complexity, facilitating easier debugging and faster development. Additionally, the clear visual representation of numbers makes it intuitive for both developers and end-users to understand the displayed information.

2. Low Cost

7-segment displays are among the most affordable components available in electronics. Their low price point makes them suitable for various applications, from hobbyist projects to mass-produced devices. This cost-effectiveness allows designers to incorporate displays into their products without significantly impacting the overall budget.

3. Versatility

These displays come in different configurations, such as common anode and common cathode, providing flexibility in design choices. They are widely used across multiple applications, including clocks, timers, and electronic meters. This versatility makes 7-segment displays an attractive option for developers looking to implement numeric displays in their designs.

4. Ease of Implementation

Implementing a 7-segment display in VHDL is relatively straightforward, allowing developers to write concise and easily understandable code. The control logic required to drive the display is simple, often involving basic case statements to map binary inputs to segment outputs. This ease of implementation supports quicker prototyping and encourages experimentation with digital design.

5. Immediate Feedback

The ability to display numerical values in real-time provides immediate feedback in various applications, enhancing user interaction. For example, in digital clocks or counters, users can quickly see updated values without any delay. This immediate feedback is crucial for applications requiring precise monitoring and control.

6. Integration with Other Systems

7-segment displays can be easily integrated with other digital components, such as counters, microcontrollers, and FPGAs. This compatibility enhances overall system functionality and allows for more complex designs. Developers can use these displays alongside other elements of their projects, providing seamless interaction within a digital system.

7. Robustness

These displays are generally designed to be durable, making them suitable for a range of operating conditions. They can withstand physical stress and environmental factors, ensuring long-term reliability in various applications. Their robustness makes them ideal for both indoor and outdoor uses, where they might be subjected to harsh conditions.

8. Reduced Power Consumption

Compared to many other display technologies, 7-segment displays tend to consume less power, particularly when displaying static information. This energy efficiency is beneficial for battery-operated devices, as it helps extend battery life and reduce overall energy costs. By using less power, designers can create more sustainable and efficient electronic products.

Disadvantages of 7-Segment Display in VHDL Programming Language

Despite their advantages, 7-segment displays have limitations that can affect their effectiveness in various applications. Recognizing these drawbacks helps designers make informed choices when selecting display technologies to meet their project requirements.

1. Limited Character Representation

7-segment displays are primarily designed to show numeric values (0-9) and a limited set of alphabetic characters (A-F for hexadecimal). This limitation restricts their use in applications requiring full alphanumeric output or complex symbols. For example, displaying letters such as ‘G’ or ‘Q’ accurately is challenging, making them less suitable for applications that demand more comprehensive character sets.

2. Lack of Flexibility in Displaying Information

The fixed structure of a 7-segment display limits how information is presented. Unlike more versatile display technologies like LCDs or OLEDs, which can display images, graphics, or varied fonts, 7-segment displays can only show predefined shapes. This restriction makes them unsuitable for dynamic content or applications needing a rich visual experience.

3. Complexity in Driving Multiple Displays

While driving a single 7-segment display is relatively straightforward, controlling multiple displays can introduce complexity. For applications requiring multiple digits, additional circuitry (like multiplexers) may be needed to manage segment activation, leading to increased design complexity and potential timing issues. This multiplexing can complicate the coding and implementation in VHDL.

4. Limited Brightness and Contrast

The brightness and contrast of 7-segment displays are generally lower than that of modern display technologies. While they can be sufficiently bright for indoor use, their visibility may diminish in brightly lit environments. This limitation can hinder their effectiveness in applications where clear visibility is crucial, such as outdoor or high-glare situations.

5. Higher Power Consumption with Multiple Displays

Although a single 7-segment display is energy-efficient, powering multiple displays simultaneously can lead to increased power consumption. As more segments are activated, the current drawn from the power supply rises, which may be a concern in battery-operated applications. This aspect necessitates careful design considerations to manage power usage effectively.

6. Parallax Errors

When viewed from different angles, parallax errors can occur, causing distortion in the perceived output. This limitation is particularly noticeable in applications where users might view the display from various positions. Such errors can lead to misinterpretation of the displayed values, affecting the overall user experience and reliability of the system.

7. Limited Visual Feedback

7-segment displays typically provide very basic visual feedback, often showing only one value at a time. In situations where a user needs to see multiple readings or statuses, additional displays or indicators may be required, complicating the design. This limitation can lead to a cluttered interface or require extra space on the device to accommodate multiple indicators.

8. Difficulty in Displaying Decimal Points

While some 7-segment displays include a decimal point segment, indicating decimal values requires careful management of segment activation. This can complicate the logic needed in VHDL to display numbers with decimal points correctly. Users may find it challenging to interpret values without clear visual cues, making it essential for designers to implement additional logic for proper representation.