20-750-DENC-1 — 755 Series Dual-Port EtherNet/IP Communication Option Card

The 20-750-DENC-1 is a dual-port EtherNet/IP communication option card for the 755 series AC drive. It installs in one of the drive's option card slots and adds two independent RJ-45 Ethernet ports, enabling both Device Level Ring (DLR) topology and standard linear/star network connections from the same drive. Once installed, the drive becomes a full EtherNet/IP node — speed commands, drive status, fault codes, and parameter access all available over the network.

The dual-port design is the key differentiator from single-port EtherNet/IP cards. A drive with one Ethernet port requires a network switch at each drive location for DLR or daisy-chain wiring. Two ports mean the drive itself acts as a passthrough device — cable goes in one port, continues to the next device out the other port. On a production line with a dozen drives spread across 50 metres of machine, that eliminates a dozen switches and their associated panel space, 24V supplies, and potential failure points.

Specifications

Parameter	Value
Part Number	20-750-DENC-1
Compatible Drive	755 Series AC Drive
Protocol	EtherNet/IP (CIP)
Ethernet Ports	2 × RJ-45, 10/100 Mbps (auto-negotiate)
Topology Support	Linear, Star, Device Level Ring (DLR)
IP Address Assignment	BOOTP, DHCP, or static (via drive HIM or software)
I/O Messaging	Class 1 cyclic (control/status)
Explicit Messaging	Class 3 / UCMM (parameter access)
DLR Support	Yes (ring node, not ring supervisor)
Installation	755 drive option card slot
Power Source	Powered from drive option slot (no external supply)
Operating Temperature	−10°C to 60°C
Standards	EtherNet/IP conformance tested, CE, UL

Dual-Port vs. Single-Port — The Practical Difference

A single-port EtherNet/IP card connects the drive to one network port. Every other device on the same network needs its own cable run to a switch. If you have 10 drives in a line, you need 10 cable runs to a central switch — plus the switch itself, its power supply, and its installation space.

With dual-port cards and DLR topology, the wiring changes fundamentally. The first drive connects to the ring supervisor (typically the PLC's EtherNet/IP port). From there, a cable exits the drive's second port and goes to the first port of the next drive. That drive's second port continues to the third drive, and so on down the line. The last drive's second port loops back to complete the ring. Ten drives, one continuous cable chain, no switches at the drive locations.

DLR adds a layer of resilience: if the cable between any two drives breaks, the ring supervisor detects the break and reroutes traffic in the opposite direction. All nine remaining drives stay connected. Cable maintenance can then be scheduled rather than becoming an emergency.

What to Monitor Once Connected

With the drive on EtherNet/IP, the controller's I/O connection gives real-time access to the drive's operating data every RPI cycle. The most useful parameters to map into the controller program for monitoring and diagnostics:

Output frequency and speed: verify the drive is actually running at the commanded speed, not just indicating "running" in the status word.
Output current: trending motor current over time reveals mechanical degradation — a pump with a developing bearing problem shows gradually increasing current before it fails.
DC bus voltage: bus voltage below nominal under load indicates an input supply issue; overvoltage indicates regenerative energy not being properly managed.
Drive temperature: the drive's internal thermal monitoring reports its heatsink temperature. An upward trend in operating temperature over weeks indicates a cooling problem developing — dirty heatsink fins, reduced panel airflow, a failing cooling fan — before it causes a thermal fault shutdown.
Active fault code: map the fault code register directly to the HMI. Displaying the actual fault number — not just "drive fault" — gives maintenance technicians an immediate diagnostic without connecting a laptop.

FAQ

Q: Can both Ethernet ports connect to different network segments simultaneously?

No. Both ports share one IP address and one network connection — they function as a two-port switch within the drive. You can't connect port 1 to one subnet and port 2 to a different subnet. Both ports are on the same network segment.

Q: Which option card slot does this card install in?

The 755 has multiple option slots with specific type assignments. Communication cards have a designated slot — the exact slot number depends on the drive frame size and which other option cards are installed. Consult the 755 option card installation documentation for the slot assignment rules before installing.

Q: What happens to drive operation if the EtherNet/IP connection is lost?

The drive executes its configured communication loss action — options include fault, coast to stop, ramp to stop, or continue at last commanded speed. Set this in the drive parameters to match the application's fail-safe requirement before commissioning.

Q: Can this card be used for parameter access (reading/writing drive parameters) in addition to I/O control?

Yes. Explicit messaging (Class 3 / UCMM) provides on-demand parameter read and write via MSG instructions from the controller. This is used for drive configuration, reading fault history, and adjusting non-time-critical parameters like ramp times and torque limits without operator access to the drive HIM.

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