Seven-segment displays are a staple in digital electronics, used to present numerical data in devices ranging from clocks to calculators. At Digilent, we incorporate these displays into several FPGA development boards, like the Nexys A7 and Arty Z7, making them ideal for both learning and teaching digital design.
What Is a 7-Segment Display?
A 7-segment display consists of seven LEDs arranged in a figure-eight pattern. Each segment is labeled A through G, and when illuminated in specific combinations, they form digits (0–9) and letters (A–F). Some displays also include an eighth segment for the decimal point (DP).
There are two main types:
- Common Anode (CA): All anodes are connected together; segments are lit by grounding their cathodes.
- Common Cathode (CC): All cathodes are connected together; segments are lit by applying voltage to their anodes.
How Digilent Boards Use 7-Segment Displays
Nexys A7
The Nexys A7 features an 8-digit 7-segment display, controlled using multiplexing. Although only one digit is lit at a time, the display cycles through all digits rapidly—faster than the human eye can perceive—creating the illusion that all digits are lit simultaneously.
Each digit includes:
- A common anode pin to enable the digit.
- Cathode pins (CA–CG, DP) to control individual segments.
To display a hexadecimal value like 85ECA921, the FPGA cycles through each digit, enabling its anode and setting the appropriate cathode signals based on the desired character. This is typically managed in VHDL using a state machine with eight states (S1–S8), each corresponding to one digit.
Arty Z7 + Pmod SSD
While the Arty Z7 doesn’t include a built-in 7-segment display, it supports external modules like the Pmod SSD, which can be connected via Pmod ports. This allows users to implement similar display logic using the Zynq-7000 SoC’s programmable logic.
The Arty Z7’s flexibility makes it a great platform for custom display projects, especially when paired with Digilent’s Pmod ecosystem.
Educational and Professional Applications
For Educators
Digilent boards are excellent tools for teaching:
- Binary-to-decimal conversion
- State machine design
- Timing and synchronization
- VHDL or Verilog programming
For Professionals
Engineers and developers can use these boards to:
- Prototype display logic for embedded systems
- Test UI concepts
- Integrate real-time data visualization into FPGA designs
Tips for Getting Started
- Refer to the Nexys A7 Reference Manual (PDF) for pin mappings and electrical characteristics.
- Explore Vivado example projects to jumpstart your development.
- Try modifying the state machine to display different patterns, messages, or animations.
Whether you’re an educator, student, or engineer, Digilent’s FPGA boards offer a hands-on way to explore how 7-segment displays work. From simple digit rendering to dynamic animations, these displays are a gateway to understanding digital logic and embedded design.
