pros & cons of RS232 vs RS485 vs ethernet

[engsatapex]

Hi all,

Thought I would post this question on eng tips. Can anyone explain the pros and cons of RS232 , RS 485 and ethernet comms protocols in terms of cost, speed, installation, ease of config, noise, cable distance...etc

 

[tygerdawg]

As I posted on another topic, as good as EngTips is, there is not a lot of controls related traffic and it pains me to redirect from here. But you may get a quicker answer at

http://www.plctalk.net/qanda/

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com

 

[danw2]

This link compares RS-232 and RS-485:

http://www.bb-elec.com/tech_articles/serial_communications_systems.asp

This link provides an overview of industrial ethernet. Make a matrix with your stated criteria and compare ethernet to the 232/485 serial transport layers

http://www.bb-elec.com/tech_articles/introduction_to_industrial_ethernet.asp

 

[PNachtwey]

Except for the fact RS-232 and RS-485 is cheaper there aren't any benefits. I prefer RS-485 over RS-232 because it can be multi drop like Profibus DP and obvious much faster and able communicate at higher rates.

Ethernet rules.




Peter Nachtwey
Delta Computer Systems

http://www.deltamotion.com

 

[jraef]

Quick and dirty comparison of those 3 choices:
RS-232 = One device to one device, very close proximity, not a lot of noise. Speed = lowest. Implementation = easy. Cost = cheapest. Applications = programing ports, one-to-one comms.

RS-485 = Multiple devices on one cable, more noise immune, thousands of feet. Speed = medium. Implementation = easy. Cost = cheap, but sometimes not as cheap as RS-232 if it was built-in (i.e. PCs). Applications = Small networked single point nodes, smart devices, SCADA, programming over small networks.

Ethernet = Virtually any number of devices, virtually unlimited distance (through various technologies), very noise immune. Speed = quantum faster than RS-485. Implementation = most difficult initially (but very common now). Cost = highest.
Applications = WANS, LANs, high speed nodes, long distance SCADA but it's often overkill for single point nodes.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[djs]

There is one "quirk" I have run into with using Ethernet. If the backbone or transport for the ethernet signal is bandwidth limited, it is usually better to use a serial (RS-232, RS-485) type communication.
One example of this is ethernet radios on a licensed band. The radio bandwidth is usually very limited, about 9600 baud. Unfortunately to make the radio behave like an ethernet switch, some of that radio bandwidth is used as overhead. So you are better off using straight serial.

 

[dV8r]

There is one "quirk" I have run into with using Ethernet. If the backbone or transport for the ethernet signal is bandwidth limited, it is usually better to use a serial (RS-232, RS-485) type communication.
One example of this is ethernet radios on a licensed band. The radio bandwidth is usually very limited, about 9600 baud. Unfortunately to make the radio behave like an ethernet switch, some of that radio bandwidth is used as overhead. So you are better off using straight serial.

This is not "True" Ethernet, portal to portal.
This is like taking a fast train from NY to LA but swimming the Mississippi.