ControlNet : Architecture, Working, Differences & Its Applications

ControlNet technology was first developed in the year 1995 by Rockwell Automation because it strives to be ahead of the recent technology trends. After that, this open industrial network protocol was handled completely by ControlNet International. However, the management & support of ControlNet was transferred to ODVA (Open DeviceNet Vendors Association) so that it handles all protocols within the Common Industrial Protocol family. ControlNet provides different features like interlocking in real-time, I/O bandwidth, peer-to-peer messaging, etc. The ControlNet network is mainly designed to enhance productivity throughout the time-critical application data transmission for both manufacturing & process automation. So this article discusses brief information on ControlNet – architecture, working, and its applications.

What is ControlNet?

ControlNet is an open industrial network protocol that uses the CIP (Common Industrial Protocol) for the higher layers from seven layers of the OSI model. The ControlNet designers adapted the CIP layers of the transport layer, network layer, data link & physical layer to fit the ControlNet network requirements.

This protocol was mainly designed to give consistent, high-speed control & I/O data transfer with programming that sets the logic to a particular time above the network. There are different devices that are communicated with this network are PLCs (Programmable Logic Controllers), HMIs, I/O chassis, drives, robots & personal computers. It is normally utilized for applications that work excellently with scheduled communications.

The data transfer speed of this network is 5 Mbps & is in the mid-range of the three famous networks through EtherNet/IP that ranges from 10Mbps – 1Gbps & DeviceNet ranges from 125 – 500 Kbps.

ControlNet Architecture

The ControlNet protocol is used in industrial automation applications. ControlNet uses the CIP or Common Industrial Protocol for facilitating interconnection between different OSI layers. This protocol is designed to provide consistent data transfer & high-speed control through the programming. So that it sets the logic to a particular timing above the network & helps in quick data transfer. This Network includes different devices such as PLCs, I/O chassis, personal computers & drivers.

ControlNet Connectors & Cables

Here, it is significant to note that the ControlNet uses RG-6 coaxial cables through the BNC connectors. The connectors used in ControlNet a BNC connectors. The BNC connector is a small easily connect or disconnect RF connector, used for coaxial cable. This connector is mainly designed to maintain cable’s similar characteristic impedance including 50 ohms & 75-ohm types being made. Generally, it is used for RF & video connections up to about 2 GHz & up to 500 volts. These connectors are simply used with small to very small coaxial cables within television, radio & other RF electronic equipment. So they were normally utilized for early computer networks like the IBM PC Network, ARCnet & the 10BASE2 variant.

ControlNet allows you to choose the types of the cable where these cables have flexible or direct burial nature. In addition, these cables are also used in any environment. Alternatively for ControlNet, there are different applications that require longer distances & also utilize optical fiber (OFC) within the cabling. Here, it is very essential to note that, it supports a maximum of 99 nodes over the network.

The nodes in the ControlNet are simply allocated through a MAC ID address. Furthermore, every node identifies the successor & predecessor address also. Every node that is available within the interface of ControlNet mainly includes a scheduled time (token). So, in this network, at a time just one node is transmitted which would ultimately avoid the collisions of data from taking unsafe propositions. If ControlNet is properly arranged, it can be extremely reliable & stable. Furthermore, it needs less maintenance over a longer period as compared to different industrial automation-based networks.

ControlNet Topology

ControlNet topologies while designing the network are trunkline-dropline, tree, or star.

Trunkline-Dropline Topology

The trunk line-drop line topology utilizes only one cable thin or thick cable. The main distance between network limits differs with the length of the cable & data speed. In this topology, the nodes can be directly connected to the main line otherwise through short branches. This topology provides twisted pair busses separately for both signal & power distribution.

Tree Topology

Tree topology is one kind of network topology that looks like a tree. This topology includes one central node & each node is simply connected to this node throughout a single lane. The main advantages of this topology are; a combination of star & bus topologies, detection of an error, durability, device support, network growth, etc. This topology is frequently used for connecting several devices like computers, printers, etc in an office or home. This topology helps in creating bus networks, wherever every device is simply connected to a middle server.

Star Topology

Star topology is a type of network topology where each device is connected individually to a central node, called the hub/switch. This topology looks like a star. This topology helps in reducing the transmission line failure impact by connecting independently every host toward the hub. Thus, every host may commune with all others through sending & receiving from the hub. please refer to this link to know more about Star Topology.

Physical Media

The ControlNet protocol physical media mainly includes Taps, Segments, Terminating resistors, Bridges & Repeaters which are discussed below.

Taps are one of the types of physical media that allows you to fix nodes to the trunk with the help of a drop cable. These are available in different types like T or Y, straight & right angle that has flexibility while configuring the ControlNet network.

At each trunk cable end, a 75Ω terminating resistor is used. The set of trunk cables known as Segments & taps have terminating resistors at every end. Each segment length mainly depends on connected devices to the trunk.

Repeaters are useful in extending the ControlNet networks by simply connecting among the segments.
Bridges are devices used between networks as communication connections. These devices forward network packet information.

Token Ring

The nodes in ControlNet are assigned a MAC ID address where every node also recognizes its successor & predecessor address. Here, every node includes a scheduled time that is decided through a token. When the node has control of the token, then it sends data frames until the token achieves its time limit. After that, a new token can be formed which is passed on to the next logical successor.

Timing

The ControlNet timing is done with a NUT or Network Update Time that depends on a permanent &repetitive time cycle. The Network Update Time is set from 2 to 100 msec duration & it includes three main parts scheduled, unscheduled & guardband. In ControlNet, the nodes include timers that are synchronized by the NUT which separates the entrée time among the nodes consistently.

Messaging

The ControlNet protocol utilizes mainly two types of messaging connected and unconnected which are discussed below.

Connected messaging in this protocol mainly uses resources in every node that are used for particular purposes like transfer of or real-time I/O data & transactions of the frequent explicit message. The resources of a connection are set aside and arranged with available communications services using the unconnected message manager.

Unconnected messaging is utilized in the establishment procedure of connection & also it is used for low-priority & rare messages. This kind of messaging uses unscheduled bandwidth always & the unconnected resources within a device are known as UCMM (unconnected message manager). To get a conformity declaration, ControlNet protocol products are necessary to execute a UCMM to accept requests from other types of devices.

How ControlNet Works?

In ControlNet, just one node can sent at a time which will prevent any data collisions from occurring. Once the node stops sending & does not get ahead of the token, then ControlNet has written conditions into it that will generate the token again & transmit it to the further logical successor. ControlNet is an open control network that meets real-time and high-throughput application demands. This protocol supports interlocking from one controller to another controller & real-time I/O control, valves & drives. It also provides control networking within process & discrete applications.

How to configure/code a microcontroller as a ControlNet node  ?

Configuring a microcontroller as a ControlNet node involves setting up the necessary hardware and software components to enable communication over the ControlNet network.  Here’s a general outline of the steps to configure a microcontroller as a ControlNet node:

• Choose a compatible microcontroller: Select a microcontroller that supports the ControlNet protocol or has the necessary hardware features like CAN (Controller Area Network) interface and a compatible transceiver.
• Obtain ControlNet communication stack: Acquire the ControlNet communication stack/library for your chosen microcontroller. The stack provides the necessary functions and protocols to enable communication over the ControlNet network.
• Hardware setup:
  • Connect the microcontroller to a ControlNet network using the CAN interface. This usually involves connecting the CANH and CANL pins of the microcontroller to the corresponding pins of a CAN transceiver.
  • Provide power supply and any other required connections to the microcontroller as per its specifications.
• Firmware development:
  • Write the firmware for the microcontroller using the ControlNet communication stack/library you obtained. This firmware will handle the communication with the ControlNet network.
  • Implement the necessary functions to handle data exchange with other devices on the ControlNet network.
• Device configuration:
  • Each node on the ControlNet network is assigned a unique node address. Ensure that your microcontroller’s node address is correctly configured. This address is used to identify the node on the network.
• Network integration:
  • Integrate the microcontroller with the rest of your control system. This might involve connecting sensors, actuators, or other devices to the microcontroller and defining how it interacts with the overall system.

What are the available ControlNet communication stack/library?

 Some of the popular ControlNet communication stacks/libraries:

• Rockwell Automation/Allen-Bradley ControlNet Stack: Rockwell Automation is a prominent provider of industrial automation and control solutions. They offer a ControlNet communication stack that is typically used with their ControlLogix programmable logic controllers (PLCs) and other automation devices.
• Anybus ControlNet Stack: Anybus, a brand of HMS Networks, provides communication stacks for various industrial protocols, including ControlNet. Their stack allows easy integration of ControlNet functionality into industrial devices.
• Softing ControlNet Stack: Softing is another company that provides industrial communication solutions. They offer a ControlNet stack that enables developers to implement ControlNet communication in their applications.
• CIP (Common Industrial Protocol) Toolkit: The CIP Toolkit is a collection of tools, sample code, and documentation provided by ODVA (Open DeviceNet Vendor Association) for implementing CIP-based protocols like ControlNet and DeviceNet.
• ProSoft Technology ControlNet Solutions: ProSoft Technology offers various industrial communication solutions, including ControlNet products and development services.

Before choosing a specific ControlNet communication stack/library, consider the following factors:

• Compatibility: Ensure that the stack/library is compatible with your microcontroller’s hardware and software platform.
• Vendor Support: Check the level of support available for the stacks used from the particular vendor.

ControlNet Vs Profibus

The difference between ControlNet and Profibus are discussed below.

Advantages

The advantages of ControlNet include the following.

• ControlNet has high speed.
• This network has deterministic data transfer.
• ControlNet is properly arranged then it is extremely reliable & stable.
• This protocol has flexible topology choices.
• It has deterministic and repeatable performance for both process & discrete applications;
• It is capable of replacing or removing nodes in power at any network point
• It needs less maintenance.
• It allows up to 99 devices for each node.
• It is very flexible & uses sophisticated data.

The disadvantages of ControlNet include the following.

• The hardware cost is high.
• Troubleshooting is very hard compared to other protocols.
• It does not provide signal & power in a single cable.

Applications

The applications of ControlNet include the following.

• ControlNet provides high-speed control, reliable & I/O data transmission with programming that sets the logic to a particular time above the network.
• This network provides critical messaging that doesn’t depend on timing to be performed without interfering with the transfer of control & I/O data.
• It is an open industrial network protocol used in industrial automation applications,
• These are open control networks that simply meet the real-time and high-throughput demand applications
• This also provides control networking within discrete & process applications.
• It is a scheduled communication network mainly designed to exchange cyclic data.
• This network also allows you to control large diffusion models for supporting extra input conditions.

Thus, this is an overview of a ControlNet. It is a network protocol used in the industrial sector. IoT & automation solutions need faster speeds, more data, and consistent data handling. So the fast speed of ControlNet will make it helpful in different applications like weld controls, vision systems, robotics, motion control, etc. This protocol is used in Time-sensitive, redundant & deterministic applications compared to Ethernet/DeviceNet. This protocol operates without a repeater up to 1000 meters, connects up to 99 devices, has a 5 Mbps of data transfer rate & provides several topologies. Here is a question for you, what is DeviceNet?