Applies To:
  • CitectSCADA 5.xx

What protocol does the new Allen Bradley Ethernet I/P equipment use and what is the CIP protocol? Is this similar to the EPIC protocol mentioned in other Citect Knowledge Base articles? 


The PLC5 and SLC500 processors communicate using PCCC (Programmable Controller Communication Commands) application-level commands. Ethernet TCP/IP connectivity was originally added to the SLC5/05 and PLC5E using the proprietary Client Server Protocol ("CSP") protocol, with embedded PCCC commands (CSP/PCCC).

Later, the ControlLogix system was developed with a new communications architecture based on the "Control and Information Protocol" (CIP). When it was first developed this was also known as EPIC. See also KB Article Q2352.

The new Allen Bradley EtherNet/IP (EIP) protocol is actually CIP over Ethernet. The EIP protocol is an open protocol and is now publicly available for download.


The present PLC5E and SLC5/05 support both CSP and EIP protocols ("dual-stack") concurrently on the same Ethernet cable at the same time. This allows support for both CSP/PCCC and EIP/PCCC commands. The RSLinx communication software normally communicates to PLC5E and SLC5/05 using the legacy CSP/PCCC protocol. RSLinx version 2.3 can be configured to communicate with PLC5 and SLC5/05 using EIP as well.

ControlLogix processors support direct, symbolic addressing of Tag data in "native" mode (i.e. without PCCC commands) using EIP explicit messages (EIP/native). For compatibility with existing serial devices, the ControlLogix also supports the use of PCCC commands (EIP/PCCC) to access Tag data that have been mapped to "compatibility files". The RSLinx communication software communicates to ControlLogix processors using EIP/native commands.


Below are the currently recommended communications drivers.

ABTCP - CSP/PCCC commands to PLC5E and SLC5/05 processors

ABRSLINX - EIP/PCCC commands via RSLinx OEM v2.3 or later, to processors using Ethernet I/P communications.

OPC - EIP/native commands via RSLinx OEM to ControlLogix processors.

CiT currently plans to develop both EIP/native and an EIP/PCCC drivers, which will not require the use of RSLinx OEM.

We will post more information here as it becomes available.