BiSS Serial Protocol

BiSS (Binary Synchronous Serial) encoders are a type of digital rotary encoder that use a high-speed, synchronous data transfer protocol to communicate position and speed information from the encoder to a controller or other device. The BiSS serial protocol is "open source", meaning any encoder manufacturer can use the BiSS protocol if they so choose. We see BiSS encoders from Hengstler, Baumer, Dynapar and many other brands. The BiSS protocol has evolved from the older SSI serial protocol. 

Here’s a quick breakdown of BiSS protocol:

1. Data Communication: BiSS uses a serial communication protocol for transmitting position data, typically over a two-wire interface (clock and data lines). It's known for providing reliable, high-speed data transfer.

2. Accuracy and Resolution: BiSS encoders offer very high resolution and precision, often used in applications that require detailed position feedback, like robotics, industrial automation, or CNC machines.

3. Real-Time Feedback: BiSS encoders provide real-time position feedback, which is critical in high-precision control systems.

4. Advantages:

   • High Speed: BiSS supports high-speed communication for quick feedback.
   • Noise Immunity: The robust design allows it to function reliably even in industrial environments with high electromagnetic interference (EMI).
   • Multidrop Capability: Multiple encoders can be connected to a single controller in a multi-drop configuration, reducing wiring complexity.

5. Applications: BiSS encoders are used in a variety of fields, such as robotics, CNC machining, automotive systems, and any industry requiring high-precision position sensing.

6. Recovery: BiSS allows easy recovery from momentary data dropouts during operation and is compatible with SSI and EnDat hardware, requiring only software changes.
7. Identification and programming: BiSS can address internal registers in the encoder that can be read by and written to by the master with data about the encoder itself (identification, device data, resolution, etc.)
8. Data transmition: BiSS encoders can also carry other digital data (temperature, etc.) and transmit the data to the master on demand, without interfering with real-time operation.

The protocol’s popularity comes from its simplicity, reliability, and high-performance capabilities, especially when compared to other protocols like SSI (Synchronous Serial Interface).

Image 1. "BiSS Encoder Communication Format". 

BiSS has two modes: sensor mode and register mode. In sensor mode, the encoder communicates similarly to SSI, with the master sending clock pulses and data being sampled once the data line drops low. BiSS can transmit data at speeds up to 10MHz, significantly faster than SSI's 1.5MHz. This faster transfer rate reduces propagation and calculation delays, enabling hardware compatibility with SSI. The main difference between the two lies in data length and framework, which can be adjusted in the software.

BiSS Encoder Mode Options

• BiSS-B: BiSS-B encoders have two distinct modes, position data and register mode. At startup, the drive instructs the encoder to send position data or toggle into register mode. Custom parameters may also be configured by an equipment manufacturer in addition to position data.
• BiSS-C: Also known as BiSS Continuous Mode, BiSS-C encoders only have one mode and break up non time critical data and sends it to the controller over several reads. This allows non time critical data to be read without going into a separate mode. The compromise is that BiSS-C startup time is slightly longer than BiSS-B. 
  It should be noted that BiSS-B and BiSS-C are not compatible with each other and should be noted when replacing an existing BiSS encoder.  
• BiSS encoder output with Sin-Cos 1Vpp: BiSS encoders can also provide a 1V p-to-p sin/cos output for real-time control, since the on-demand absolute encoder data can come in too slowly for many control loops.

Hengstler BiSS - Example Ordering Information

AD34

AD35

AD36

AD38