CRC Calculation in Ethernet | Serial CRC Using LFSR Explained

Why It Matters

Understanding CRC calculation and its hardware implementation is essential for designing reliable Ethernet interfaces and ensuring data integrity across high‑speed networks.

Key Takeaways

• CRC appends zeros equal to polynomial degree before division.
• Modular division using XOR yields remainder as CRC bits.
• LFSR implementation uses flip‑flops tapped per polynomial coefficients.
• Receiver recomputes CRC; zero remainder validates the frame.
• For CRC‑32, parallel techniques replace serial LFSR due to speed.

Summary

The video walks through Ethernet’s Frame Check Sequence, showing how a cyclic redundancy check (CRC) is calculated using a serial Linear‑Feedback Shift Register (LFSR). It starts with the Ethernet frame structure, then explains that the sender appends a number of zero bits equal to the polynomial’s highest degree before performing modular division. Key steps include selecting a generator polynomial, appending zeros, and executing XOR‑based division to obtain the remainder, which becomes the CRC bits. The presenter demonstrates the process with a 4‑bit data example and a 5‑bit polynomial, detailing each XOR operation and how the remainder is formed. A hardware‑focused segment maps the algorithm onto five flip‑flops, assigning taps where the polynomial coefficients are one. The video shows how feedback and XOR gates drive the register through successive clock cycles, producing the final CRC value after the last data bit is shifted in. Finally, the instructor notes that while the serial LFSR illustrates CRC fundamentals, real‑world Ethernet (CRC‑32) relies on parallel implementations to meet speed requirements, underscoring the practical relevance of efficient error‑checking circuitry.

Original Description

In this video, we discuss how CRC (Cyclic Redundancy Check) is generated in Ethernet using a Serial LFSR (Linear Feedback Shift Register) approach.

CRC is one of the most important concepts in Ethernet communication because it helps detect transmission errors in Ethernet frames.

🔍 In this session, we cover:

✔️ Introduction to Serial CRC

✔️ Why LFSR is used for CRC calculation

✔️ Polynomial-based CRC generation

✔️ Step-by-step Serial CRC example

✔️ XOR feedback operation in LFSR

✔️ Shift register working principle

✔️ CRC generation in Ethernet MAC

💡 This video is highly useful for:

VLSI Engineers

FPGA Developers

Verilog/SystemVerilog Learners

Protocol Design Engineers

Digital Design Students

📌 Upcoming videos will cover:

➡️ Parallel CRC Calculation

➡️ CRC Generator RTL Design

➡️ Verilog Implementation of LFSR-Based CRC

👉 Subscribe for the complete Ethernet MAC Controller Design Series from basics to RTL implementation.

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