| Allen-Bradley have allowed us to reproduce
the following article: "Important information about Ethernet
including: connectivity to legacy products, the role of ASA
messaging, and EPIC and CSP protocols." It contains a series of
questions and answers. Additional relevant comments with respect to
Citect and the CSP and EPIC protocols have been added, for which
Allen-Bradley takes no responsibility. See also KB article Q2223.
Question
What is CSP?
Answer
CSP is the "Interchange Client-Server Protocol". CSP is an
application level protocol that is layered on top of TCP/IP and
uses a standard socket level interface. TCP/IP provides a reliable
byte-stream, over which CSP provides a set of commands and message
formats that are used to encapsulate PCCC messages. CSP was
originally designed for Ethernet-TCP/IP communications between
Interchange software and the Pyramid Integrator. CSP was later
implemented in the PLC-5E, the Ethernet Sidecar and the SLC 5/05
processor for communications among Ethernet products over TCP/IP.
CSP was not designed to support ASA messaging over TCP/IP, so it
was inadequate to support the communications requirements of the
ControlLogix architecture, which uses ASA messaging. Citect's ABEI
and ABTCP drivers support the CSP protocol.
Question
What is "EPIC"?
Answer
EPIC is the "Ethernet Protocol Interface
for Controllers". It is an application-level protocol that was
designed to support ASA messaging over TCP/IP. EPIC is layered on
top of TCP/IP, and uses a standard socket level interface. TCP/IP
provides a reliable byte-stream, over which EPIC provides a set of
commands and message formats that are used to encapsulate ASA
messages. EPIC was specifically designed to support the
requirements of ASA messaging over TCP/IP, in order to support
Ethernet-TCP/IP communications with the ControlLogix platform.
Future versions of Citect's ABEI driver will support the EPIC
protocol.
Question
Are EPIC and CSP open, standard
protocols?
Answer
EPIC and CSP were developed internally for Rockwell Automation
products, thought they make use of standard, open TCP/IP protocols.
EPIC was originally based on, and is compatible with, the protocol
used by RSLinx. Responsibility for maintaining compatibility
between EPIC and RSLinx is shared between Allen-Bradley and
Rockwell Software.
Question
What are "legacy processors"?
Answer
The term "legacy processors" as used in
this KB article refers to the PLC-5 family, including the PLC-5C's,
PLC-5E's and the Ethernet Sidecar, and the SLC-500 family including
the SLC-5/05 Ethernet processor.
Question
Why is Allen-Bradley now using EPIC?
Answer
EPIC was invented to support ASA messaging over Ethernet-TCP/IP,
and to enable Rockwell Automation Ethernet products to take full
advantage of the features of the ControlLogix platform. Some of
these features are:
- communication with 1756-ENET modules in any slot of the
ControlLogix chassis.
- peer-to-peer messaging between legacy processors or
workstations on Ethernet and legacy processors on ControlNet
through the ControlLogix Gateway.
- peer-to-peer messaging between legacy processors or
workstations on Ethernet and devices on DeviceNet through the
ControlLogix Gateway (future functionality).
- peer-to-peer messaging between legacy processors or
workstations on Ethernet and legacy processors on DH+ through the
ControlLogix Gateway.
- peer-to-peer messaging between legacy processors or
workstations on Ethernet and the Automation Controller.
These features are based on ASA messaging and are unique to the
ControlLogix architecture. EPIC's predecessor, the CSP protocol,
was inadequate to support these features. Therefore, EPIC was
created.
Question
Which products currently use EPIC?
Answer
The 1756-ENET module is the first firmware-based product to
incorporate EPIC. RSLinx, starting with the AC0 ControlLogix
Gateway release, supports EPIC.
Question
Which products currently use CSP?
Answer
Firmware-based products that use CSP are: the PI Ethernet Interface
module, the PLC-5E, the Ethernet Sidecar, the PLC-5 Control
Coprocessor, and the SLC 5/05.
Question
Are there any products which support EPIC that will not support
CSP?
Answer
Yes, the ControlLogix Ethernet module, 1756-ENET, will not support
CSP - only EPIC.
Question
Is the ControlLogix Gateway a "drop-in" replacement for the PI
Gateway?
Answer
No. The ControlLogix Gateway was not
designed to be a "drop-in" replacement for the PI Gateway. It was
designed to support bridging of ASA messages between an Ethernet
network the ControlLogix system, which is ASA-based. Customers of
Ethernet legacy products who are unable to upgrade their
applications to the ControlLogix Gateway should continue to
purchase the PI Gateway for their applications.
Question
Which products are planned to be
upgraded to use EPIC?
Answer
The PLC-5E, the Ethernet Sidecar and the
SLC 5/05 are all planned to support EPIC for communications with
the ControlLogix platform (tentative delivery in Q2 FY98). The PI
Ethernet Interface module (5820-EI ) and the PLC-5 Control
Coprocessor are not planned to support EPIC.
Question
How will the legacy processors in the
field be upgraded to support EPIC?
Answer
PLC-5E processors prior to series E will
require an EPROM firmware upgrade. The PLC-5E (series E or beyond),
the Ethernet Sidecar, and the SLC 5/05 use Flash memory and can be
upgraded in the field.
Question
Is it necessary for Rockwell Software
products to support EPIC?
Answer
Any Rockwell Software product that is
required to communicate from a workstation on Ethernet through the
ControlLogix Gateway will need to support EPIC. Any Rockwell
Software product that is required to communicate from a workstation
on Ethernet to the Logix5000 or to any module in the ControlLogix
chassis will need to support EPIC. Otherwise, it is not necessary
to implement EPIC.
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