The controller and all of its remote I/O, files, and other devices talk to each other through the network in a ControlLogix system. How good this link is is very important. If your network is slow or unstable, it will affect how well the controls work. On the other hand, if you have the right network, the system will be responsive, stable, and easy to manage. So, picking between networks like ControlNet and EtherNet/IP is a big choice that will affect both how well your system works now and how much it can grow in the future.
ControlNet uses fixed cycles called Network Update Intervals (NUIs). Devices are given times each turn to send or receive data. This plan makes things more predictable. That way, modules like the 1756-OB32 output card or the 1756-IB32 input module can rely on steady timing in their data exchange. The network works like a bus or a straight line, and coaxial cable is often used to connect nodes in a row or with short taps.
| Strengths | Weaknesses |
|---|---|
| Consistent timing and low jitter | Bandwidth capped at 5 Mbps; not enough for large data loads |
| Simple or no switches; fewer active devices | Fixed topology, limited flexibility in wiring |
| Good for small, stable I/O islands | Hard to scale or change later |
| Robust for outdoor or harsh environments (proven) | Many new devices no longer support ControlNet directly |
Also, modules like 1794-ACN15 that use ControlNet require the network to maintain strict scheduling. If many devices try to share the same cycle, performance may degrade.
EtherNet/IP employs the Common Industrial Protocol (CIP), which is related to ControlNet and DeviceNet. It divides communication into two types: implicit messaging for quick I/O data and explicit messaging for configuration and diagnostics. A module like the 1794-AENT sends Flex I/O data over regular Ethernet lines; therefore, a coaxial cable is rarely required for remote I/O.
Modern support: Many new I/O modules, drives, and safety devices are designed for EtherNet/IP.
Controllers that support EtherNet/IP can connect directly. That means parts of a ControlLogix system can bypass older bus networks and connect over IP.
The following table highlights how ControlNet and EtherNet/IP differ in important dimensions relevant to ControlLogix systems.
| Feature | ControlNet | EtherNet/IP |
|---|---|---|
| Maximum throughput | 5 Mbps fixed limit | Typically 100 Mbps or more |
| Timing control / jitter | Very strong due to fixed cycles | Good with QoS, time sync mechanisms |
| Network layout & cabling | Coax or specific media, limited branches | Ethernet wiring, fiber, stars, rings |
| Number of nodes / growth | Limited by schedule and media | Many nodes via IP addressing |
| Device support | Mostly older, fewer modern modules | Wide support for I/O, motion, safety |
| Diagnostic tools | Basic tools and traffic analyzers | Rich tools via managed switches, SNMP, etc. |
| Redundancy & failover | Redundant media in some cases | Redundancy is more flexible via PRP, ring, switch redundancy |
| Migration / expansion ease | Harder to change once built | Easier to expand and adapt |
| Security & future readiness | Minimal security features | Supports CIP Security, better IT/OT alignment |
In systems that use modules like 1785-L80E or others tied to older bus networks, going with EtherNet/IP often gives more breathing room for growth and integration.
In a ControlLogix system, certain modules guide the network decision more than others. Use these hints when designing or upgrading.
When using a high number of I/O modules, such as the 1756-IB32 and 1756-OB32, EtherNet/IP can better handle volume and future growth demands.
For mixed or transitional states, it may make sense to keep some of the system on ControlNet while expanding additional regions on EtherNet/IP.
Choose a network that matches current modules while allowing for future changes.
These steps reduce risk and help ensure performance stays acceptable during transitions.
A fixed bandwidth of 5 Mbps is what ControlNet can handle. A bus-based method means that only one device can send at a time during a cycle. Multiple devices can send data at the same time with EtherNet/IP because it uses network switches and parallel lines. This makes the flow of EtherNet/IP much faster.
Yes. A ControlLogix rack can hold multiple network modules. This lets some parts work on ControlNet and others on EtherNet/IP. Bridges or routers let them talk to each other. Traffic doesn’t get in the way of other networks when there is good planning.
Not all the time. ControlNet might be enough if the system only needs a small amount of information and the cycles are short. EtherNet/IP has more space for systems that need to handle more data or that are planning to grow. To switch to EtherNet/IP, you need to carefully plan the network layout, switch settings, and delay.
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