Comunnication between PLC

Hi
First of all thak you all for your posts in my other threads, you have been a great help!

Does any one have information about types of plc's comunnication?
how it happens, the diferences between protocols, etc etc etc....

I dont know much about this subject but i hope with your help i can become a little more educated!

Thank you
zezito

Hello zezito;
First look at the "communication" portion of the PLC tutorial on this webpage (Learn PLCs).
For comparision values between different fieldbuses, look up this site:http://www.synergetic.com/compare.htm
or
http://www.epanorama.net/links/tele_interface.html
Then try different manufacturers/fieldbus sites: profibus.com, modbus.org, as-interface.com, odva.org (for devicenet), phoenixcontacts.com (for Interbus-S)...

Hope this helps,
Daniel Chartier

That's a pretty broad question.

Would you like a list of protocols? That's been posted before.

If you want technical descriptions, pick a few protocols and ask again.

Are you interested in any specific transmission medium: ethernet, radio, infrared, RS232/485, etc?

What do you want your communication bus to do: error checking, speed, supply power, security, noise immunity, machine safety?

AK

To me, protocol is just like language we human used to communicate between each other; some of us know English, some know Russian, etc...and most of us know more than one language. Same with language used by machines whether it be a PC, Mainframe, or PLC. Most PC knows TCP/IP, SMTP, IPX, etc. For two machine to talk to each other, each must speak the same language (protocol). Anyhow, that's a very simplifed view of protocol.

Thank you for your posts!

i wanna know why people use diferent types of protocols, how do they choose wich one is best for their aplication. what are the bennefits of using each protocol, in a few words...i want to learn about this issue!

So...please let me know any site, book/manual , or even just give me your idea/advice in how to choose that!

thank you

zezito said:

i wanna know why people use diferent types of protocols, how do they choose wich one is best for their aplication.

Click to expand...

Well, in that case my reply applies (I made a funny).

We chose a protocol, hopefully, that is suited to our application. Some protocols are friendly and play well with all types of equipment. Other protocols are biggoted and only want to talk to specific types of equipment. We choose a protocol that is supported at all points in the network or subnetwork that we are developing. Sometimes, you only have one choice.

If we select equipment that gives us more communication options (or select a communication option that mandates a new choice of equipment), we can choose to evaluate the protocol based on robustness, cost (of equipment and installation), ease of use, or the COLOR of the cable used for network connections.

If you're looking for more detailed information, try doing a search here and on the web for the following:
Ethernet
DeviceNet (see also CAN)
Modbus
Foundation Fieldbus (aka. H1)
Profibus
DF1
DH+
DH485
RemoteIO
ASCII Data

Also, look for:
RS232
RS485
Modems
Radio
Cat5
Fiber

AK

Well, are you trying to get more info in term of theory or you have a specific problem with choosing a protocol?

I can't help you much with the theory side. In my experience it's rarely a problem to select a protocol in real life because usually you DO NOT have a choice. Especially when it comes to the industrial automation world. It's more of an issue for the IT side of things, each protocol have it's advantages and disadvantages, some are more fault tolerant and some offer better error checking (remember the old days with 300 baud modem? phone noise make garbages comes on the screen, eek) For the control stuff, hardward and software limitation usually limits the choice for protocol. For example, a DH+ HMI can only talk to a DH+ equipped PLC or via a bridge of some sort. The most common problems are incompatible protocol/hardwares, it's no wonder that a lot of the post here deal with "how do I make X talk to Y" because someone is handed two piece of old equipment that are not designed to talk to each other.

Also sometime it's the ease of setup that determines which protocol to use, as in the case of DH+ vs Remote IO for Allen Bradley products as discuss in this thread: http://www.plctalk.net/qanda/showthread.php?s=&threadid=9646&highlight=dh*

Try this one. It should keep you busy for hours.
Fieldbus Website

Thank you all for your replies!!

i'm sure that your advices will help get more educated about this subject!

Thankx again for you help!
Zezito