RS-232 Recommended Standard 232

What is RS-232?

RS-232 — Recommended Standard 232

The RS-232 (Rec­om­mend­ed Stan­dard-232) or also known EIA-232 (Elec­tron­ic Indus­tries Alliance-232) is a stan­dard for the ser­i­al trans­mis­sion of data in indus­tri­al applications.

The stan­dard defines the elec­tri­cal char­ac­ter­is­tics and tim­ing of sig­nals, the mean­ing of sig­nals, and the phys­i­cal size and pinout of connectors.

  • First intro­duced in 1960, RS-232 used to be the main stan­dard for ser­i­al ports for com­put­ers and is still wide­ly in indus­tri­al appli­ca­tions today.
  • It defines the sig­nalling between a DTE (data ter­mi­nal equip­ment), such as a pro­tec­tion relay, and a DCE (data cir­cuit-ter­mi­nat­ing equip­ment or data com­mu­ni­ca­tion equip­ment), such as an RTU.

  • RS-232 is only used for point-to-point com­mu­ni­ca­tions, i.e. it only sup­ports com­mu­ni­ca­tions between two devices as for exam­ple a mas­ter and a slave device in a Mod­bus network.

  • The max­i­mum speed of RS-232 is around 115Kbps with a max­i­mum dis­tance between net­work devices of about 30m.

  • So it has some draw­backs in com­par­i­son to lat­er devel­oped inter­faces such as RS-422, RS-485 and Eth­er­net, such as a large volt­age swing, large con­nec­tors, no mul­ti­point capa­bil­i­ty, lim­it­ed mul­tidrop capa­bil­i­ty and the lim­i­ta­tions in terms of trans­mis­sion speed and range.

Ethernet vs RS-232 vs RS-422 vs RS-485

It is impor­tant not to con­fuse com­mu­ni­ca­tion pro­to­cols with stan­dards for elec­tri­cal char­ac­ter­is­tics of phys­i­cal com­mu­ni­ca­tion media. Dif­fer­ent com­mu­ni­ca­tion media are used depend­ing on project needs. The stan­dards’ main dif­fer­ences are the com­mu­ni­ca­tion speeds, the max­i­mum num­ber of con­nect­ed devices and the phys­i­cal dis­tance between con­nect­ed nodes.

RS-232
The RS-232 (Rec­om­mend­ed Stan­dard 232) or also known EIA-232 (Elec­tron­ic Indus­tries Alliance-232) stan­dard is used only in point-to-point com­mu­ni­ca­tions, i.e. it only sup­ports com­mu­ni­ca­tions between two devices, which in the case of the Mod­bus pro­to­col would be a mas­ter and a slave device. The max­i­mum speed of RS-232 is around 115Kbp/s with a max­i­mum dis­tance between net­work devices of about 30m.

RS-422, or also TIA/EIA-422, was intend­ed to replace the old­er RS-232C stan­dard with a stan­dard that used dif­fer­en­tial sig­nalling to pro­vide high­er speeds, longer cable lengths and less noise. At short dis­tances, data trans­mis­sion rates can reach up to 10 Mbit/s. At low­er rates, data can be send through cables with a length of up to 1,500 meters.

RS-485
The RS-485 (Rec­om­men­dad Stan­dard-485) or EIA-485 (Elec­tron­ic Indus­tries Alliance-485) stan­dard is one of the most wide­ly used stan­dards for ser­i­al com­mu­ni­ca­tion in indus­tri­al appli­ca­tions. The main dif­fer­ence with RS-232 is that it allows more than two devices on the net­work, enabling to have sev­er­al slaves. It achieves rates of up to 12Mbps and in rar­er cas­es up to 50Mbps, while the max­i­mum dis­tance with­in the net­work is 1200m, and the max­i­mum num­ber of devices on the net­work is 32.

Eth­er­net
Depend­ing on the vari­a­tion used, tran­simis­sion speeds with Eth­er­net range from 100Mbps and up to 10Gbps, while max­i­mum dis­tance can vary from 100m to 200m depend­ing on project con­di­tions and the type of cable used. In some cas­es, it is pos­si­ble to use fiber optic net­works, which enable longer dis­tances and high­er com­mu­ni­ca­tion rates, as well as wire­less communication.

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    Communication Interfaces

    The RS-232 (Rec­om­mend­ed Stan­dard-232) or also known EIA-232 (Elec­tron­ic Indus­tries Alliance-232) is a stan­dard for the ser­i­al trans­mis­sion of data in indus­tri­al applications.

    The stan­dard defines the tim­ing, elec­tri­cal char­ac­ter­is­tics and mean­ing of sig­nals as well as the phys­i­cal size and pinout of connectors.

    The RS-485 (Rec­om­mend­ed Stan­dard-485) or also known EIA-485 (Elec­tron­ic Indus­tries Alliance-485) stan­dard defines the char­ac­ter­is­tics of an elec­tri­cal inter­face for ser­i­al com­mu­ni­ca­tions in indus­tri­al con­trol systems.

    In con­trast to the old­er RS-232, it allows to bal­ance elec­tri­cal sig­nals and con­nect mul­ti­ple device to the net­work, which can stretch over longer dis­tances and harsh­er environments.

    The RS-422 (Rec­om­mend­ed Stan­dard-422) or also known EIA-422 (Elec­tron­ic Indus­tries Alliance-422) stan­dard defines the char­ac­ter­is­tics of an elec­tri­cal inter­face for ser­i­al com­mu­ni­ca­tions in indus­tri­al con­trol systems.

    It was designed to replace the old­er RS-232C stan­dard in order to pro­vide high­er speed (up to 10 Mb/s), bet­ter immu­ni­ty from noise, and longer cable lengths (up to 1,500 meters).

    100BASE-FX is a phys­i­cal lay­er spec­i­fi­ca­tion for Fast Eth­er­net over fiber optics using two mul­ti-mode fiber optic strands for both links, recep­tion and transmission.

    The max­i­mum length is 412 meters for half-duplex con­nec­tions (to ensure that col­li­sions are detect­ed) or 2 kilo­me­ters for full-duplex.

    100BASE-TX is the most com­mon Fast Eth­er­net phys­i­cal lay­er, trans­mit­ting data through two twist­ed wire-pairs (one for each direc­tion), which pro­vide full duplex oper­a­tion with 100 Mbit/s of through­put in each direction.

    Cabling dis­tances are lim­it­ed to 100 metres (328 ft) for each net­work segment.

    RS-232 & iGrid

    All iGrid devices can be ordered with dif­fer­ent con­fig­u­ra­tions of Eth­er­net and ser­i­al ports, includ­ing RS-232, RS-422, RS-485 and fiber optics amongst oth­ers. We have expe­ri­ence with all kinds of pro­to­col con­ver­sions from and to ser­i­al com­mu­ni­ca­tion standards.

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