BiSS (Bidirectional Synchronous Serial Bus) is a high-speed, real-time communication protocol mainly used for industrial automation and motion control systems. Created by the German company iC-Haus, BiSS is designed to achieve fast, bidirectional communication between sensors, actuators, and controllers, especially in applications requiring precise data exchange, such as CNC machine tool rotary encoders and position sensors, robots, and other high-precision equipment.
Key features and mechanisms
The BiSS protocol operates on full-duplex, synchronous serial interfaces, allowing for continuous data streams between a master device (such as a controller or PLC) and multiple slave devices (such as sensors or actuators). Unlike traditional protocols, BiSS can achieve data rates of up to 10Mbps, making it suitable for applications requiring high-speed and low-latency data exchange. It is compatible with the RS-422 and RS-485 physical layers, providing robust long-distance communication. Typical configurations involve a master device sending clock signals to the connected slave devices to synchronize data exchange.
The protocol is renowned for its configurational flexibility. BiSS supports point-to-point and bus configurations. In a point-to-point setup, the master device communicates with a single slave device, commonly seen in simple configurations. For more complex arrangements, bus configuration or daisy chaining allows multiple slave devices to be connected sequentially, with data passing from one device to the next. This structure promotes high scalability in industrial environments for coordinating multiple sensors or actuators on the same network, enabling them to synchronize data transmission while minimizing wiring complexity.
Communication framework and data integrity
The data communication of the BiSS protocol is structured around a communication frame that includes multiple key components:
Master Clock (MA) – The master device sends clock pulses to control data synchronization.
Data signal – responds to the device response clock signal in the form of data, which may include sensor readings, error flags, or status updates.
Timeout and line delay adjustment – BiSS compensates for potential signal delay (usually referred to as line delay) in longer cable distances, ensuring data accuracy and consistency in time-sensitive operations.
This framework structure, combined with real-time error detection mechanisms such as CRC (Cyclic Redundancy Check), can maintain high reliability of the protocol even in typical electrical noise environments in industrial settings.
BiSS variant: BiSS-B and BiSS-C
BiSS has evolved into multiple versions to adapt to different usage scenarios. BiSS-B is an older variant that provides basic unidirectional communication and is mainly used for simpler systems. The more advanced BiSS-C is a full-duplex version that supports data transmission in both directions from the master to the slave and vice versa, thus enabling real-time feedback and monitoring. BiSS-C is widely used in applications that require continuous monitoring and high-speed data transmission, as it allows for efficient closed-loop control in automated systems.
Comparison with other protocols
BiSS is usually compared with other industrial protocols such as SSI (Synchronous Serial Interface) and EnDat. Although SSI provides direct serial communication, it lacks the speed and bidirectional capability of BiSS, making it less suitable for high-speed or complex setups. On the other hand, EnDat also supports bidirectional communication, but it is usually more proprietary. In comparison, BiSS remains an open protocol, providing flexibility for integration with various devices and encouraging broader industry adoption.
In summary, the BiSS protocol is designed for industrial automation applications that require fast, reliable, and bidirectional data exchange, especially in systems with multiple high-precision sensors or actuators. Its openness, high-speed performance, and adaptability to complex configurations make it the preferred choice for modern motion control and robotic systems.