•TECHNOLOGY OVERVIEW SERIESCIP on TDMA Technology

PUB00161R1 MARCH 2016

CompoNet™ – CIP on TDMA
CompoNet™ is a field network designed for applications
dominated by distributed field devices, each with few I/Opoints. It features high-speed communication, provides
flexible topology, reduces wiring labor, and helps to cut
down on troubleshooting and maintenance work. CompoNet
is a member of a family of networks that implements theCommon Industrial Protocol (CIP™) at its upper layers.
CIP encompasses a comprehensive suite of messages
and services for a variety of manufacturing automation
applications, including control, safety, synchronization,motion, configuration, diagnostics and information. As a truly
media-independent protocol that is supported by hundredsof vendors around the world, CIP provides users with unified
communication architecture throughout the manufacturing
enterprises.
With media independence comes the ability to choose aCIP Network best suited for each application. One of these
possible choices is CompoNet, which adapts CIP to TDMA
(Time Domain Multiple Access) on a simple 2-wire physicallayer. TDMA assures each device a fixed time slot in thecommunication cycle, resulting in low overhead and strict
cycle times. This efficiency allows large numbers of nodes toshare small amounts of data, without requiring extremely highbaud rates. As a consequence, CompoNet can reliably run on
inexpensive unshielded 2-wire cable.
CompoNet offers several unique advantages for automation
applications: ast cyclic exchange of bit- and word-sized data,F
making it a high performance network for sensors
and actuators.

• yclic I/O data which can be distributed over up toC384 nodes.

• IP messaging, allowing intelligent field devices toC
be configured and maintained remotely.

• wide range of data rates (93.75kbps to 4Mbps),
A
allowing a flexible trade-off between speed anddistance.

• -wire flat cables allowing easy installation, or cost4
efficient unshielded 2-wire cable.

•• ata collection applications where ease ofD
communications via EtherNet/IP™ to plant hostcomputers is a must.

Here’s a more in-depth look at the technology behind every
CompoNet-compliant product.

What is CompoNet?
CompoNet, like other CIP Networks, follows the Open Systems
Interconnection (OSI) model, which defines a framework forimplementing network protocols in seven layers: physical,
data link, network, transport, session, presentation andapplication. Networks that follow this model define a complete
suite of network functionality from the physical implementation
through the application or user interface layer. As with all CIP
Networks, CompoNet implements CIP at the Session layer
and above while adopting CompoNet specific definitions at
the Transport layer and below. This network architecture isshown in Figure 1.
By employing a subset of all available CIP functions, andsome simplifications in the Transport Layer, CompoNet
implementation is significantly ‘lighter’ than other networks.
Yet, while still being a lower layer of the CIP Network
family, CompoNet is still able to provide all basic functionsof CIP. Implementation of the Session layer and above isfundamentally the same as other CIP Networks with only
minimal adaptations.
CIP Motion™
ProfilesMotor Control
Profiles•2 ire-savingWinmodularmachines.
Withsubmillisecond cycle times at the higher baud rates,a single flat cable can link machine modules without
loss of performance.

OtherProfiles

I/OProfiles

Semiconductor CIP Safety™
ProfilesProfilesObject Library(Communications, Applications, Time Synchronization)

SafetyObject Library

Data Management Services
Explicit and I/O Messages

Safety Servicesand Messages

Originator Services
for Modbus® Device
Integration

Connecting Management, Routing

TCP/UDPInternet Protocol

Typical applications of CompoNet are:Transducer
ProfilesCompoNet
ControlNet
DeviceNet
Network and Transport Network and Transport Network and Transport

Ethernet
CSMA/CD

CompoNet
Time Slot

ControlNet
CTDMA

CAN
CSMA/NBA

Ethernet
Physical Layer

CompoNet
Physical Layer

ControlNet
Physical Layer

DeviceNet
Physical Layer

EtherNet/IP™

CompoNet™

ControlNet™

DeviceNet™

Figure 1: CompoNet as Part of the CIP OSI Model

Network Adaptations of CIP

 p to 64 repeaters, enabling a large number ofU
nodes and coverage of wide areas with complex
topologies.

 onveyor and warehouse applications. With I/OC
points few and far apart, the free network topology
at the low baud rate will cut down wiring cost.
Repeaters can extend the covered area.

Common Industrial Protocol (CIP™)••

The Physical Layer
CompoNet’s physical layer was derived from RS485
specifications. The use of Manchester signal codingtechnology along with a pulse transformer in the physical layer
improves the reliability of the communication. These additions
make it possible to use cheap unshielded cables. The pulse
transformer isolates each device from the communicationline and reduces signal disturbance. The pulse transformer isconnected in a fashion that enables the doubling of transmit
voltages, while requiring lower threshold voltages on thereceive side. This technique increases the magnitude of thesignal at the receiving end.
In addition, CompoNet implements a special “Receive mask.”
The mask is accomplished using advanced digital signal
filtering. This allows the use of cables of different electricalcharacteristics, and realizes transmission in various data
rates. Receive masks have following features.
• educed voltage and skewed signals can be moreR
readily and reliably be received and decoded.

• oise rejection of spike and reflected waveforms isN
greatly increased.

CompoNet network technologies allow the use of dedicatedrepeaters. Repeaters extend the maximum trunk line lengthand expand the installation area. Furthermore, they greatly
increase the number of connectable nodes, and allow mixed
use of different types of cables.
As shown in Figure 2, repeaters can extend the maximum
trunk line length to three times the standard length. Use ofmaximum 64 repeaters can expand the installation area,and allow the connection of a large number of nodes. The
repeaters divide the network into multiple layers, and allow
the mixed use of flat and round cables. This enables various
topologies such as cost-effective round cables for the trunkline and easy to install flat cables for sub-trunk lines.
In addition, TDMA minimizes the transmission delay due torepeaters, and decreases its influence on the communication
cycle. Key to the use of repeaters is the ability of the remoteslaves to “know” their location in the network, and transmit
I/O data just before it is required on the backbone. There is,therefore, no delay in communication with the master due todelays in the response of the slaves.

Figure 2	  TECHNOLOGY OVERVIEW SERIES: COMPONET
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CompoNet
topology
exampleFigure2: CompoNet
topology
example3

The Data Link Layer
MAC (Media Access Control) generates and analyzes theCompoNet communication frames.The MAC layer has thefollowing functions to satisfy CompoNet transmission quality
and high-speed.
•Manchester coding•

CRC generation/check• dding a special preamble (a start code) toA
accomplish no gaps (zero inter-frame delay betweenframes). This means that there is none of the idle timeon the wire that is typical of some other networks.

Transmission direction
Preamble

Command CodeCommand-dependent block

On a CompoNet network, IN and OUT frames can be usedin variable sizes as to the number of I/O points. This is toaccomplish network efficiency. Moreover, multiple MAC IDs
are provided separately for bit node and word node. This
improves usability and simplifies the implementation forvendors.
The CompoNet protocol provides several functions to improve
maintainability, in addition to I/O and explicit messaging.
• athering slave information by CN frame. It notifies
Gthe master of an error state of slave through 4-bit
flags embedded in the data frame.It can detect anerror state without signaling from master.

• etting slave information by STR (Status read byGB_EVENT frame). STR indicates which nodes areconnected to which repeaters. This information
enables the tools to understand the network
configuration and get a sense of its topology.

• TR also provides information that describes a slave.
S
Such information includes vendor ID, device type
and product code. By reading STR data stored in
the master, the tools can speedily scan the network
configuration and collect detailed information about
all devices connected to it.

• aud rate synchronization by BEACON frame. TheB
master notifies a slave of its baud rate. This allowseasy synchronization.

CRC

Manchester encoding

Figure 3: Frame block

TDMA (Time Domain Multiple Access) controls the CompoNet
frame transmission and reception. In the CompoNet network,the master controls frames on the wire at optimal states inorder to improve the network efficiency. There are 7 typesof frames in CompoNet such as OUT, TRG, BEACON, CN,IN, A_EVENT and B_EVENT frames. The master directly
controls OUT, TRG, BEACON, A_EVENT and B_EVENT
frames. However, it does not control CN and IN frames thatare sent by slaves. The master sets the appropriate, optimizedtiming for the slave to send those frames, at the time the slave
participates in the network. The timing being described is theperiod of time after receiving an OUT or a TRG frame for aslave to transmit its data.
One of the main characteristics of TDMA is the minimizationof transmission delay due to repeaters. With some othernetworks, a substantial transmission delay occurs at a repeater
since it typically receives, reforms, and resends the signals, inorder to properly capture and check the frames. Therefore, arepeater delay must be considered in the frame transmission
timing. A gap must be provided between frames to avoid theircollision. For example, if 2 repeaters are used in a network,
the required gap will be four times of a repeater delay period.
CompoNet requires no gap between frames by having theCN and IN frames restrict the repeaters to transmit data only
through a master port to a slave port (Repeat operation fromthe slave port is not allowed. It must go back through themaster.) CN and IN frames are sent out to the wire earlier tooffset delays caused by repeaters.

4Application layer
Presentationlayer

Session layer
Transport layer

CompoNet
LINK

Application

Message
RouterUCMM

Network layer

CompoNet
Event manager

Data link layer

Media AccessController

Physical layer

Identity

I/O
Connection

I/O interface

Low level linkmanager

TDMAPHY

Figure 4: OSI Layer details

The Network andTransport Layer
Because CompoNet uses UCMM (Unconnected MessageManager) to send or receive the explicit message protocol,
the master must be aware of the existence of the destination(slave) in advance of sending it messages. Furthermore,
the master must establish the transmission timing of IN andCN frames to slaves prior to sending the frames. Therefore,
CompoNet controls slave participation (as participated state
or non-participated state) in the Transport layer.
The master detects the existence of slaves through CNframes. When master receives a CN frame from nonparticipated slave, it automatically processes the participation
state of the slave. STR or STW (Status write by B_EVENT frame) is used for participation processing. Explicit
messages (A_EVENT message) are sent to the slaves whoare in the participated state. STW is to notify the slave ofCnTimeDomain, InTimeDomain and OutBlockPointer, which
are required for implementing TDMA. In accordance with thereceived TimeDomain notification, the slave responds with anIN frame and a CN frame, and then retrieves its OUT datafrom the OUT frame.
After the participation process, an explicit message thenimplements allocation of the Predefined connection set. Whena slave in participated state does not respond to CN framesor IN frames for an extended period of time, then the masterregards the slave to be in the network timeout state.
The I/O interface passes on IN or OUT data between
TDMA and upper layers. The IN and OUT data are updated
automatically by TDMA. The I/O interface gets IN data andtransmits OUT data for TDMA. TDMA manages allocation ofOUT data via the OUT frames. The I/O interface reallocates
the OUT data which are transferred by the upper layer to theformat managed by TDMA.

The Upper Layers
CompoNet uses the Common Industrial Protocol (CIP), astrictly object-oriented protocol, at the upper layers. Each
CIP object has attributes (data), services (commands) andbehaviors (reactions to events).
CIP also defines “device types” which includes “deviceprofiles.” The device profile specifies the set of CIP objects thatmust be implemented for a given device type, the configuration
options and the I/O data formats. This consistency in object
implementation per device type has several advantages.
Users of CIP Networks can promote a common applicationinterface for a given device type, and increase interoperability
in networks comprised of devices from multiple vendors. Thevendors can add specific objects to a CompoNet-compliant
product, and support the functional requirements of particularapplications.
Seamless bridging and routing is perhaps the most significant
advantage for users of CIP Networks. It is this mechanismthat most benefits the user’s investment for the future. The
ability to originate a message on one CIP Network, such as
EtherNet/IP, and then pass it to another CIP Network, suchas CompoNet, with no presentation at the Application Layer,means that users can incorporate incremental application
improvements to existing installations and/or integrate
automation systems with diagnostic, prognostic and/or IT
applications. Seamless bridging and routing between bothhomogeneous and heterogeneous CIP Networks is enabled
by a set of objects that defines routing mechanisms for a device
to use when forwarding the contents of a message producedon one network port to another. This mechanism does notalter the contents of a message during the routing process.
When using this mechanism, the user’s only responsibility is
to describe the path that a given message must follow. CIP
ensures that the message is handled correctly, whichever theCIP network type is involved.

The CompoNet Event manager controls the explicit message
fragmentation. It also monitors the responses and retries
to send the explicit messages in its unique manner, sinceCompoNet uses UCMM to send and receive the explicit
messages. The CompoNet Event manager buffers the explicit
messages sent by the upper layers. It requests TDMA to send
Events. Before sending a request to TDMA, it divides a longexplicit message into smaller fragments.
TDMA notifies the CompoNet Event manager of the explicit
message response. A long response is divided into smaller
fragments when the CompoNet Event manager receives it.
The CompoNet Event manager recomposes the fragments toan explicit message response, and sends the whole message
to the upper layer. The CompoNet Event manager monitors
the responses. When there is no response for an extended
period of time, the CompoNet Event manager either retries
the sending of the message or it processes a time-out.

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Management of theCompoNet Technology
CompoNet is managed by ODVA, an international
association of the world’s leading automation companies.
ODVA’s CompoNet management responsibilities include:•Publishing The CompoNet Specification;•

 verseeing the process to incorporate newO
enhancements to The CompoNet Specification;• icensing the CompoNet Technology to companies
Ldesiring to make and/or sell CompoNet-compliant
products;•

 romoting industry awareness of CompoNet andP
its benefits; and•

 elping to ensure compliance of CompoNet
H
products with the specification through conformance
testing and conformity reporting.

For more information about CompoNet, CIP or ODVA, visit
ODVA at www.odva.org.

6About ODVAFounded in 1995, ODVA is a global association whose members
comprise the world’s leading automation companies. ODVA’s mission
is to advance open, interoperable information and communication
technologies in industrial automation. ODVA recognizes its media
independent network protocol, the Common Industrial Protocol or “CIP” –and the network adaptations of CIP – EtherNet/IP, DeviceNet, CompoNet
and ControlNet – as its core technology and the primary common interestof its membership. ODVA’s vision is to contribute to the sustainability
and prosperity of the global community by transforming the model for
information and communication technology in the industrial ecosystem.
For future interoperability of production systems and the integration of theproduction systems with other systems, ODVA embraces the adoptionof commercial-off-the-shelf (COTS) and standard, unmodified Internet
and Ethernet technologies as a guiding principle wherever possible. This
principle is exemplified by EtherNet/IP – the world’s number one industrial
Ethernet network. For more information about ODVA, visit odva.org.

ODVA

Ann Arbor, Michigan, USA
TEL: +1 734-975-8840
FAX: +1 734-922-0027
WEB: www.odva.org
PUB00161R1©1999-2016 ODVA, Inc.

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