• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer

Motion Control Tips

Automation • Motion Control • Power Transmission

  • News
    • Industry News
    • Editor Blogs
    • Video
  • Controls
    • HMIs
    • PC-Based Controllers
    • PLCs + PACs
    • Stand-Alone Controllers
    • Software
  • Drives
    • Servo Drives
    • Stepper Drives
  • Encoders
    • Absolute Encoders
    • Incremental Encoders
    • Rotary Encoders
  • Mechanical
    • Bearings
    • Brakes + Clutches
    • Belt + chain
    • Couplings
    • Gears + Gearing
    • Lubrication
    • Shock + Vibration Mitigation
    • Springs + Rings + Seals
  • Linear
    • Actuators
    • Linear Motors
    • Linear Encoders
  • Motors
    • AC Motors
    • DC Motors
    • Brushless Motors
    • Gearmotors
    • Piezo Motors
    • Servo Motors
    • Stepper Motors
  • Systems
    • Conveyors + linear transport systems
    • Gantries + Stages
    • Rotary Tables
    • Grippers + End Effectors
    • Robotics
  • Networks
    • Connections + Sliprings
    • Fieldbuses
    • I/O
    • Sensors + Vision
  • FAQs
    • Motion Casebook
    • Motion Selection Guides
  • Suppliers
You are here: Home / FAQs + basics / Absolute encoder interfaces: Differences between SSI, BiSS, Hiperface, and EnDat

Absolute encoder interfaces: Differences between SSI, BiSS, Hiperface, and EnDat

April 2, 2021 By Danielle Collins Leave a Comment

Absolute encoders can communicate with controllers through parallel or serial wiring, over a fieldbus, or via an Ethernet-based protocol such as EtherCAT. Of these options, serial communication is a simpler solution than parallel wiring (which requires a twisted pair of wires for each bit of output) and is well-suited for applications that aren’t complex enough to justify a fieldbus or Ethernet-based protocol. Here, we’ll look at the differences between four of the most common absolute encoder serial interfaces available today: SSI, BiSS, Hiperface DSL, and EnDat 2.2.

SSI: Synchronous Serial Interface

As its name suggests, SSI is a synchronous protocol, meaning that data is transferred from the encoder to the controller synchronously via a clock signal, or pulse, provided by the controller. The encoder output can be in binary or gray code, and one bit is transmitted per clock pulse, with standard word lengths of 13 bits for single-turn encoders and 25 bits for multi-turn encoders.

absolute encoder interfaces
The SSI encoder interface is simple, with just four wires for communication (a twisted pair for data and a twisted pair for clock signals) and two wires for power.
Image credit: AccuCoder

Synchronous Serial Interface uses two pairs of twisted wires for communication, per the RS-422 standard — one pair for differential data signals and one pair for differential clock signals. There are also two wires for power to the encoder. The clock frequency, or rate of data transmission, can be up to 1.5 MHz, depending on the length of the cable. To ensure data integrity, some SSI encoders support multiple transmission (also known as “multi-path” or “ringshift” transmission), in which the same data is sent multiple times and the controller compares the transmissions to ensure they match.

BiSS: Bidirectional Synchronous Serial Interface

The Bidirectional Synchronous Serial Interface is an open protocol and is similar to SSI in that data transmission is synchronized by clock signals from the controller, but with BiSS, clock speeds up to 10 MHz are possible. BiSS also uses two twisted pairs of wires — one pair for data signals and one pair for clock signals — plus two wires for power.

Unlike SSI, which only supports unidirectional communication, BiSS supports bidirectional communication, meaning the controller can read from and write to non-volatile memory in the encoder, where registers contain encoder identification information. BiSS encoders can also send data, such as temperature, to the controller on demand. Another unique feature of BiSS versus SSI is that within each data cycle, the master determines and compensates for any transmission delay, allowing data transmission rates up to 10 Mbps.

The most current version of BiSS is BiSS-C (C = Continuously), although the interface is typically referred to as simply “BiSS.”

absolute encoder interfaces
BiSS allows bidirectional communication, and so uses two wires for communication from the controller (MA+ and MA-) and two wires for communication from the encoder (SL+ and SL-), plus two wires for power.
Image credit: Texas Instruments

Unlike SSI encoders, BiSS encoders can be connected point-to-point or via bus. When connected via bus, the data from all the encoders is clocked (synchronized) to the master in one continuous frame rather than individually. BiSS also implements a cyclic redundancy check (CRC) for error checking — a more reliable method than multiple transmission. There also exists a BiSS Safety interface, for safety applications up to SIL3 per IEC 61508.

Hiperface DSL

Hiperface DSL, the HIgh PERformance InterFACE Digital Servo Link, was originally a proprietary interface developed by SICK. However, in 2016, SICK “opened up” the interface with a licensing model that allows other manufacturers to integrate the technology into their product offering.

Unlike its predecessor, Hiperface, Hiperface DSL is an all-digital protocol that uses just two wires for bi-directional communication and encoder power, bundled with the motor power cable (although a transformer is required to improve the common mode noise rejection). This gives the advantage of eliminating the need for separate encoder connections on the motor and the controller. Hiperface DSL complies with the RS-485 standard and and has a data transmission rate of 9.375 Mbaud. Data can be transmitted cyclically (as fast as possible) or synchronously with the controller clock.

Hiperface
Hiperface DSL includes channels for position feedback, parameter exchange, process data, safe position, and condition monitoring (SensorHub) data, all transmitted on two wires which can be integrated into the motor cable.
Image credit: Sick

The Hiperface DSL architecture also includes channels for the transfer of motor parameter data, condition monitoring data, and integrated safe motion, with data being transmitted over two digital communication wires. This redundancy and error-checking make the Hiperface DSL interface compliant with SIL3 safety standards.

EnDat 2.2

The Encoder Data, or EnDat 2.2, interface from Heidenhain is a synchronous, bidirectional standard that uses four wires for communication — two wires each for differential data and differential clock signals — plus two wires for power and two for either battery buffering or parallel power supply. EnDat 2.2 can provide clock frequencies of up to 2 MHz, and on some models, additional compensation for propagation delay makes frequencies up to 16 MHz possible.

Since Hiperface DSL has become an “open” interface, EnDat is now the only serial interface for absolute encoders that remains proprietary (although it should be noted that the original Hiperface protocol also remains proprietary). 

With propagation delay compensation, EnDat 2.2 can supply clock frequencies up to 16 MHz.
Image credit: Heidenhain

EnDat 2.2. can also read, write, or update information stored in the encoder and can transfer data such as sensor information or diagnostic information from the encoder to the controller. The type of data transmitted — for example, absolute position, diagnostics, or parameter information — is sent via mode commands from the controller to the encoder. Like BiSS and Hiperface DSL, EnDat 2.2. is also compliant with SIL3 safety standards.

You may also like:

  • Hiperface
    What are Hiperface and Hiperface DSL?

  • Part 3: Trends in Ethernet, PoE, IO-Link, HIPERFACE, and single-cable…
  • sine encoder
    What is a sine encoder (aka sine-cosine encoder)?
  • multi-turn encoder
    What happens when a multi-turn encoder reaches 4096 turns?
  • wire an absolute encoder
    FAQ: What are the ways to wire an absolute encoder…

Filed Under: Absolute Encoders, Encoders, FAQs + basics, Featured

Reader Interactions

Leave a Reply Cancel reply

You must be logged in to post a comment.

Primary Sidebar

MOTION DESIGN GUIDES

“motion

“motion

“motion

“motion

“motion

“motion

“motion

“motion

POWER TRANSMISSION REFERENCE GUIDE

RSS Linear Motion Tips

Subscribe Today

RSS Featured White Papers

  • Identifying Best-Value Linear Motion Technologies
  • Learn how to reduce noise and distortion in encoders’ signals
  • Helical Planetary Gearboxes: Understanding The Tradeoffs
Tweets from https://twitter.com/Motion_Control/lists/motion-control-tweets

Footer

Motion Control Tips

DESIGN WORLD NETWORK

Design World Online
The Robot Report
Coupling Tips
Linear Motion Tips
Bearing Tips
Fastener Engineering

MOTION CONTROL TIPS

Subscribe to our newsletter
Advertise with us
Contact us
About us
Follow us on TwitterAdd us on FacebookAdd us on LinkedInAdd us on YouTubeAdd us on Instagram

Copyright © 2021 · WTWH Media LLC and its licensors. All rights reserved.
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media.

Privacy Policy | RSS