Serial data transmission standards

- overview of the standards for serial data communications including RS232 (RS-232), RS422 (RS-422), RS423 (RS-423), and RS485 (RS-485)

Serial data formats for the transmission of data, including RS232, RS422, RS423, and RS485 find many uses within data communications and networking. Although serial formats are not as fast as parallel formats, they are often more suitable because the cables require less constituent wires and as a result they are much cheaper and more flexible than their parallel equivalents. This enables them to be used for longer cable runs and in areas where thicker cables would not be applicable.

The first of the RS standards was RS232, or more correctly RS-232. This was developed in 1962 when the need for forms of transmitting data from modems attached telephone lines to remote communications equipments became apparent. The 'RS' stands for Recommended Standard, although later these standards were formally adopted by the EIA / TIA in the USA. The EIA is the Electrical Industries Association and the TIA is the Telecommunications Industries Association. Once RS-232 was established an equivalent standard was written for the ITU (International Telecommunications Union) to provide a more international standard. This would enable the same standards to be used worldwide and also give manufacturers access to a global market using just one product. This standard was known as V.24 and is totally compatible with RS-232.

With RS232 well established and the need for faster communications and over longer distances, further standards beyond RS232 were introduced. Although a number of standards were introduced, the most widely used are RS-422 and RS485.

RS232 summary

RS-232 is the most widely used serial standard that is in use. Many laptop computers incorporate a serial interface, and it was also used on many printers, although much less so now.

  • Cabling - single ended
  • Number of devices - one transmit and one receive
  • Communication mode - full duplex
  • Maximum distance - 50 feet at 19.2 kbps
  • Maximum data rate - 19.2 kbps at 50 feet
  • Signalling mode - unbalanced
  • Mark (1) - -5 to -15 V
  • Space (0) - +5 to +15 V
  • Output current capability - 500 mA

RS422 summary

This standard gives a much higher data rate than RS232, but it uses differential transmission techniques. Many RS422 devices are compatible with RS232.

  • Cabling - differential
  • Number of devices - five transmitters and ten receivers
  • Communication mode - full duplex / half duplex
  • Maximum distance - 4000 feet at 100 kbps
  • Maximum data rate - 10 Mbps at 50 feet
  • Signalling mode - balanced
  • Mark (1) - 2 V to 6 V max. (B>A)
  • Space (0) - 2 V to 6 V max. (A>B)
  • Output current capability - 150 mA

RS485 summary

RS-485 is a standard that allows high speed data transmission along with multiple transmitters and receivers and this makes it able to be incorporated as a network solution.

  • Cabling - differential
  • Number of devices - 32 transmitters and 32 receivers
  • Communication mode - half duplex
  • Maximum distance - 4000 feet at 100 kbps
  • Maximum data rate - 10 Mbps at 50 feet
  • Signalling - balanced
  • Mark (1) - 1.5 V to 5 V max. (B>A)
  • Space (0) - 1.5 V to 5 V max. (A>B)
  • Output current capability - 250 mA

Each of these standards meets a different requirement. RS232 still being very widely used despite the fact that it has been in use for over 40 years. However the other standards that have been introduced more recently provide higher levels of performance that are very useful in may applications.

Further information on these and other standards can be access through the Telecommunications and networking homepage.

By Ian Poole

Read more popular data communications tutorials . . . . .

Ethernet RS-232 RS-422 RS-449
RS-485 Serial data comms USB Current loop

Share this page

Want more like this? Register for our newsletter

Refining IoT Technology to Address Demands of the Healthcare Market Mark Patrick | Mouser Electronics
Refining IoT Technology to Address Demands of the Healthcare Market
The Internet of Things, IoT is destined to affect many areas of everyday life - we expect it will include many areas like smart meters, remote control of lighting, but what about the healthcare market . . .
Online - Effective Spectrum Analyzer Measurements
Learn how to make spectrum analyzer measurements at RF and microwave frequencies

More training courses

LTE Advanced Pro and Road to 5G
Chapter 1 of the new book by Dahlman et al on the latest cellular developments and current 5G status. Get this free download.

More whitepapers
 is operated and owned by Adrio Communications Ltd and edited by Ian Poole. All information is © Adrio Communications Ltd and may not be copied except for individual personal use. This includes copying material in whatever form into website pages. While every effort is made to ensure the accuracy of the information on, no liability is accepted for any consequences of using it. This site uses cookies. By using this site, these terms including the use of cookies are accepted. More explanation can be found in our Privacy Policy