BiSS – a CAD Jockey’s Guide

If you’re trying to understand what BiSS is, but are being confused by a load of technical jargon, this short paper’s for you.

BiSS is a communications system used in industrial automation. It’s a way of exchanging digital data between different parts of a control system such as a position sensor and a motor controller. BiSS is often used in robotics, machine tools and electric actuators.

BiSS is an acronym from BiDirectional Serial Synchronous…..what this means will become clearer shortly.

Importantly, BiSS is an ‘open’ system – in other words, anybody can use and implement it. This contrasts with proprietary or closed communications systems such as Hiperface or EnDat which require you to buy a particular manufacturer’s products.

BiSS was first shown by the German chip company IC Haus in 2002. It faced a bunch of patent disputes with people who didn’t want an open system on the market, but the cases were dropped in 2012. Since then, unsurprisingly, BiSS has been gaining market share at the expense of closed, proprietary systems. It is an increasingly popular choice and the reasons for its popularity are that it’s:

  • Open source
  • Economical – it only needs a few wires
  • Fast
  • Secure – it’s not easily corrupted by electrical noise or power outages
  • Easy to use
  • Suitable for safety related applications – because it includes various checks, warnings and error messages.

Originally, there were two forms: – BiSS-B and BiSS-C. Hardly anybody uses BiSS-B and it’s basically died a death. BiSS-C is the one that lots of people are using. The C part stands for Continuous. So now BiSS is nearly always termed BiSS-C by pretty much everybody – most of whom will never have heard of BiSS-B.

BiSS-C sometimes gets confused with another popular communications system – SSI (Serial Synchronous Interface). There are some similarities and BiSS-C will run using the same cables and connectors as SSI. The hardware for SSI is usually referred to as ‘RS-422 compatible’ and that’s what BiSS-C uses. RS-422 is an electrical standard which defines stuff like voltage levels etc. SSI is also a widely used communications method in the automation industry but it’s pretty much only used with absolute position sensors. BiSS-C is used for positions sensors and lots of other stuff too.

There are 2 forms of BiSS-C: unidirectional and bidirectional. Basically, unidirectional involves the control unit spitting out data to the required BiSS format when triggered by a clock signal from the host system. The control unit is usually referred to as the slave and the host system is referred to as the master.

Bidirectional is more complicated and can involve sophisticated data exchanges between multiple slave units on a bus.

The ‘serial’ part of BiSS refers to the data being sent out as a series of 1s and 0s along the data lines. The ‘synchronous’ part of BiSS refers to the data being synchronised by a clock signal – in other words a signal which triggers the transmission of data.

OK, got the gist of BiSS? That’s about it for this paper because from here onwards, further discussion requires a different approach involving detailed technical nitty gritty terms like ‘isochronal’ and ‘XML device’. I hope this basic description helped you feel a little less confused.

An example of an angle encoder offering unidirectional BiSS-C communications can be found here.

Fig 1 – Zettlex IncOders offer unidirectional BiSS-C communications

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