BiSS-C and SSI Encoder Interface Protocols Explained

March 5, 2025

BiSS (Bidirectional Synchronous Serial) Interface, specifically the BiSS-C variant, is an open-source, real-time serial protocol designed for high-speed, bidirectional data transmission. Developed to improve upon traditional serial interfaces, BiSS-C supports efficient communication with absolute encoders, sensors, and other automation components.

BiSS-C Key Features

• High-Speed Communication: Supports clock rates up to 10 MHz, making it suitable for high-performance applications.
• Bidirectional Data Transfer: Allows reading encoder data and writing configuration parameters, enabling advanced diagnostics and system flexibility.
• Open Protocol: Unlike proprietary interfaces like EnDat and Hiperface, BiSS is an open protocol, reducing licensing costs and increasing adaptability.
• Real-Time Performance: Supports cyclic data exchange for real-time motion control applications.
• High Data Integrity: Implements CRC (Cyclic Redundancy Check) to ensure error detection and data integrity.
• Multi-Slave Support: Allows connection of multiple devices in a daisy-chain configuration, reducing wiring complexity.

BiSS-C Applications

• Robotics and industrial automation
• CNC machines and precision positioning systems
• Semiconductor manufacturing
• High-speed motor feedback systems

SSI Protocol Overview

Synchronous Serial Interface (SSI) is a widely adopted serial communication protocol primarily used for absolute encoders. SSI is a unidirectional interface where the encoder transmits position data to the controller upon request.

SSI Key Features

• Unidirectional Communication: Data is transmitted only from the encoder to the controller, with no ability for configuration or diagnostics.
• Fixed Data Length: Typically supports 13-bit to 32-bit data formats, making it reliable for simple position feedback.
• Moderate Speed: Operates at clock rates between 100 kHz and 2 MHz, suitable for many automation applications but slower than BiSS-C.
• Simplicity and Compatibility: SSI is easy to integrate into existing systems due to its straightforward architecture.
• Noise Immunity: Uses differential signaling (RS-422) for robust data transmission in industrial environments.

SSI Applications

• Industrial automation and PLC-based control systems
• Elevator and conveyor systems
• Basic position feedback in motion control
• Automotive and medical applications requiring absolute positioning

Comparison of BiSS-C and SSI

Key Takeaways

• BiSS-C is a more advanced, high-speed, and flexible protocol with bidirectional communication, making it ideal for real-time applications requiring diagnostics and configuration.
• SSI is a simpler, unidirectional protocol known for its robustness and ease of integration, suitable for applications that do not require advanced features.
• The choice between BiSS-C and SSI depends on the application’s needs: if high-speed, real-time data exchange with configurability is required, BiSS-C is preferred. For simpler and reliable position feedback, SSI remains a viable option.

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