PLC Communications


Thread Starter


Can anyone please tell me of where are we at in the world now with communications in different PLC architectures, specifically AB.
> Can anyone please tell me of where are we at in the world now with communications in different PLC architectures, specifically AB.

Allen-Bradley communication choices are many these days. For years AB has supported the DH485, DH+, and Remote I/O standards. Typically the DH networks were for uploading and downloading programs and data exchange between PLC's or the Enterprise computer system. Remote I/O would bring remote discrete and analog I/O back to the PLC.

Today Rockwell (AB) supports Ethernet at the Enterprise level, ControlNet at the Automation and Control level and DeviceNet at the device level.

Ethernet and TCP/IP are used where the Enterprise needs to collect data from systems on the factory floor and is non-deterministic.

ControlNet is a 5Mbit/s network that allows Deterministic I/O to be scheduled between PLC's and other PLC's or Remote racks. Unscheduled traffic such as Upload/Download and Messaging can be done on ControlNet also. Unscheduled traffic is not dterministic.

Devicenet runs at up to 500K baud and is typically implemented at the Device level. Devicenet allows sensors imbedded with Devicenet technology to send signals to a PLC with no remote chassis involved. Although you can have remote I/O chassis on devicenet.

TO learn more go to and select NETWORKS on the pull down.

Hope this helps a little.


Ty Huband
PLC Specialist
Eck Supply Company
Lynchburg, VA
What are you looking for?

AB PLC hardware natively supports DH-485 (aka Data Sidewalk) DH, DH+, RS-232, Ethernet (10baseT), and whatever the old PLC-2 had on it. Using add on modules, you can pick up a number of
other protocols.

Is there anything specific that you are looking for?

--Joe Jansen

Dave Ferguson

If you are talking AB, the varieties are still endless. You can use an ethernet processor, or an ethernet sidecar and communicate via that. You can install a profibus card and communicate that way.

You can use either DH+ or controlnet (AB's own "semi" deterministic "producer/consumer protocol.

We unfortunately have a number of protocols being used but after a lot of thought I have moved to a mostly ethernet communications protocol. I still pass some data via DH+, I have a controlnet
network for drives installed by a vendor, I have a profibus protocol for burner control of IR burners on a paper machine coater.

I have found that the ethernet network is very reliable but it took a while to get built the way I wanted it. We have a separate fiber network with 10/100 managed switches and VLAN'd sections of the control network. This seams very stable with collision and broadcast controls in placed although rare.

If you would like more info e-mail direct at [email protected].

Dave Ferguson
Blandin Paper Company
DAVCO Automation