help please

any help with this guys?
i'm new to plc so i was wondering what types of protocol are used for communicatin between plc's.
thanks alot guys
steve

It depends on the brand of PLC.
Each one is different.

some examples I have seen:
Modbus, modbus plus, ethernet, MPI, RS232, RS485, profibus and standard, bitwise, PLC i/os.

Each PLC usually has between 5 to 10 different protocols available.

Doug

ur destination is so vast of protocol

there r several plc protocle
RS-232
RS-422
RS-485
TCP/ip
DH+
DH485
Modbus+
DNP-3
SNP
DP
MPI
P2P
it all depends on ur application and mack of PLC
may b i m wrong
i m using siemens and GE fanuc including AB
u may find all info with in this site or u may fond concern MAnufecturee SItes
ok
TC
Muhammad Faisal Qureshi

There are many protocols, and equally many misunderstandings of what is and what isn't a 'protocol'.

Things like RS232, RS422, RS485 are most definitely NOT protocols. These are all electrical standards defining signals levels etc. The fact that 2 PLCs both have an RS232 port doesn't mean they can necessarily communicate.

Likewise some protocols like Modbus were originally defined as purely that : protocols. The message structure and permissible content was described. No mention was made of the medium to be used for transmitting these messages. So here you could have two PLCs which each understood Modbus messaging, but one only had a RS232 interface, and the other only had RS485. Still no communication.

We have seen the emergence of larger standards like Profibus which defines everything : messaging, addressing, electrical standards, installation requirements, cable specs, everything. This was deliberately done to the extent that test specs were possible : does a device comply with the standard or not? There are approved Profibus test labs around the world, and if you get a certified Profibus DP slave and a certified Profibus DP master you can be *certain* they will communicate. There aren't many other standards which get you that far. Even Ethernet (which is a physical/elelctrical standard) plus TCP/IP (which are the protocol parts) may or may not get you where you want.

Overall, if all your comms is between PLCs of one manufacturer take advice from them of their recommended peer-to-peer strategy. If you intend to mix PLCs of different makes, you have to check first of all which comms standards (not just protocols) they all claim to support. This will probably reduce your choices to one or two methods. Research what each manufacturer claims are the pros and cons in their systems for these methods and match these up with your own requirements (e.g. ease of installation or troubleshooting; high speed data transfer; low programming overhead, whatever). Finally get a demo from these manufacturers of how well they can integrate with this plan. You may find this radically alters your view of which PLCs to use!

Good luck

Ken.