Can you do two things at once? Full-duplex RS-485 transceivers can.

Although it can be hard for some people to do two things at once, for electronic communications, it’s just part of the job. In fact, simultaneous two-way communication, referred to as full-duplex transmission, is nothing new.  Just as your phone or Internet connection can send and receive data simultaneously, full-duplex RS-485 transceivers have been doing this for decades. For some industrial networks, half-duplex RS-485 transceivers do the job just fine, and they can save the cost of the four-wire bus. So why is there growing demand for full–duplex RS-485 transceivers? 

RS-485 is the go-to physical layer transceiver for long industrial networks, and where the need for longer reach is compounded with higher bandwidth needs, a full-duplex RS-485 transceiver with high data rates can help achieve higher throughput. Although there are higher bandwidth full-duplex technologies like LVDS (low voltage differential signaling) or Ethernet, the RS-485 standard provides for more robust data transmission in noisy environments. This is important for networks that may run the data bus adjacent to power lines or where individual power supplies may power different nodes on the bus. These scenarios, common in industrial networks, can give rise to higher ground differences and their associated common mode voltages. RS-485 can cope with significantly higher common mode voltages of -7V to +12V, compared to the +0.2V to +2.2V range of LVDS or -1V to 3.4V for multipoint LVDS (MLVDS). 

The growth of full-duplex RS-485 transceivers likely has more to do with the “speed” portion of high speed than the bandwidth that comes with it. If your network needs to send and receive commands as fast as possible, high signaling rates, combined with simultaneous transmit and receive capability, can ensure network communication is highly deterministic. With extremely fast rise and fall times and very low propagation delays, this is important to ensure the integrity of the signals that are being transmitted. Time-critical applications, such as position encoders for motor control or enterprise data centers’ rack-to-rack communications, benefit from very low propagation delays with extremely fast rise and fall time while maintaining signal integrity.

Fellow TIer Thomas Kugelstadt visits some of these topics and more in his latest article in Design World on full-duplex transceivers.

Additional resources:

  • Learn more about RS-485 transceivers by downloading our updated RS-485 selection guide, which includes the newest 3.3V full-duplex RS-485 transceivers.
  • See this TI Design reference design for interfacing to a BiSS position encoder for motor control, featuring the new 3.3V full-duplex SN65HVD77 RS-485 transceiver.