Connecting 2 AB PLCs via serial link

[andre_k]

Hi all,

I need to get two AB PLCs (CompactLogix) communicating with each other over a serial link (RS 422), if anyone has performed this could you please point me to an example so as not to waste time ‘reinventing the wheel’ or provide me with a resource tool that would assist.

 

[TheStarr]

Why? Ethernet would be faster, easier, less problematic, and probably cheaper.

 

[SNK]

I guess if you were attempting to save money, you could do what you are asking....

I don't really think that that was the intent of AB for the serial port...

But, you could I guess communicate back and forth the old fashioned way....

VIA ASCII.

Not a pleasant way to do things. The serial port IMO was designed to communicate to other ASCII devices, not other brother PLC's.....

Good luck regardless.

 

[Ken Roach]

Get the Instruction Set Reference and read up on the MSG instruction.

There's no problem exchanging tags between controllers using the serial port.

For the best results, get an RS-232/422 converter that has hardware handshaking so you don't get into duplex issues or have to resort to DF1 Half Duplex protocol.

 

[SNK]

I learn something new every day here.
I have gone through the MSG Instruction, but I cannot see anything about setting up the serial ports....It maybe in the actual manual.

Why on earth would we ever spend $899 each for Ethernet/DH+ cards, so that we can provide comms when the Serial port is Free?

This is definitely news to me. Good news.
Siemens MPI uses the serial port...and works very quickly....

Thanks Ken.

 

[andre_k]

AB serial comms

Why? Ethernet would be faster, easier, less problematic, and probably cheaper.

I need to communicated underwater using sonic modems which only use this protocol

 

[andre_k]

Get the Instruction Set Reference and read up on the MSG instruction.

There's no problem exchanging tags between controllers using the serial port.

For the best results, get an RS-232/422 converter that has hardware handshaking so you don't get into duplex issues or have to resort to DF1 Half Duplex protocol.

I believe I will be going this way are there any traps for new players that you can think of?

 

[andre_k]

I guess if you were attempting to save money, you could do what you are asking....

I don't really think that that was the intent of AB for the serial port...

But, you could I guess communicate back and forth the old fashioned way....

VIA ASCII.

Not a pleasant way to do things. The serial port IMO was designed to communicate to other ASCII devices, not other brother PLC's.....

Good luck regardless.

Going with Ken's advice of using the R232/422 converter and simply exchange tags between controllers are there any traps for young players that you can see implementing this form of peer-to-peer communication