In short
Step-by-step engineering guide for replacing the legacy Allen-Bradley 20-COMM-ER EtherNet/IP dual-port adapter in PowerFlex 7-class drives while preserving DLR topology.
Overview
The Allen-Bradley 20-COMM-ER is a legacy EtherNet/IP Dual-Port communication adapter designed for PowerFlex 7-Class variable frequency drives (VFDs). Operating on the Drive Peripheral Interface (DPI) protocol, this adapter enables native EtherNet/IP communication, remote programming, and real-time control. Crucially, the "R" in the catalog number denotes Device Level Ring (DLR) capability, allowing the module to act as a node within a fault-tolerant, ring-topology network.
As Rockwell Automation has transitioned the 20-COMM family to obsolete or "End of Life" status, industrial facilities must plan for replacement strategies. This guide provides a comprehensive technical breakdown of the 20-COMM-ER, details direct and migration replacement options, and provides standard procedures for physical installation, parameter programming, and system commissioning.
Legacy Product Information
The 20-COMM-ER serves as the primary gateway for legacy PowerFlex drives to communicate over modern Industrial Ethernet networks without requiring separate external media converters or DIN-rail mounted switches.
Key Specifications:
- Catalog Number: 20-COMM-ER
- Protocol: EtherNet/IP (Implicit I/O and Explicit messaging)
- Interface: DPI (Drive Peripheral Interface)
- Data Rate: 10/100 Mbps (Full or Half Duplex)
- Physical Ports: Two (2) RJ45 copper ports (internal 2-port embedded switch)
- Network Topologies: Device Level Ring (DLR), Daisy-chain, Linear, and Star
- Power Consumption: 350 mA at 5V DC (supplied from the host drive's DPI port)
- DPI Connection Speed: 125 kbps or 500 kbps (automatically configured by the host drive)
Primary Host Drives:
- PowerFlex 70 / PowerFlex 70EC
- PowerFlex 700 / PowerFlex 700VC
- PowerFlex 700H
- PowerFlex 700S
- PowerFlex 700L
- PowerFlex 753 / 755 (via the 20-750-20COMM-F1 adapter card, though not common for new designs)
Recommended Replacements
When a 20-COMM-ER fails, industrial operators have several replacement pathways depending on system lifecycle strategy and budget constraints.
| Legacy P/N | Recommended Replacement | Type | Notes |
|---|---|---|---|
| 20-COMM-ER | 20-COMM-ER (Surplus/Refurbished) | Direct Swap | The fastest and least disruptive option. Requires zero changes to the PLC logic (Studio 5000/RSLogix 5000 API) or network layout. Preserves the DLR ring structure. |
| 20-COMM-ER | 20-COMM-E (Single Port) + 1783-ETAP | Functional Workaround | If a 20-COMM-ER is unavailable, a single-port 20-COMM-E can be used alongside a 1783-ETAP (EtherNet/IP Tap) to convert the single port to a DLR tap. Requires manual reconfiguration of the IP and minor cabinet space for the ETAP. |
| 20-COMM-ER | Drive Migration (PowerFlex 755TS or 753 + 20-750-ENETR) | System Upgrade | Complete hardware migration. Replaces the legacy PowerFlex 7-Class drive with a modern PowerFlex 750-series drive using a 20-750-ENETR dual-port option. Requires physical rewiring, PLC configuration changes, and drive commissioning. |
Compatibility Considerations
Replacing a 20-COMM-ER requires careful examination of several standard hardware and software facets to prevent system mismatch errors.
Wiring & Physical Footprint
- Port Layout: The 20-COMM-ER mounts directly inside the drive’s control pod or cover, or externally via a 20-XCOMM-AC-PS1 external mounting kit.
- Cabling: Cat5e shielded twisted-pair (STP) cabling with RJ45 connections is highly recommended to mitigate the electromagnetic interference (EMI) typical within VFD enclosures.
Software & Firmware
- Add-On Profiles (AOP): If swapping with a direct replacement 20-COMM-ER, the PLC program (RSLogix 5000/Studio 5000) does not require modification.
- Electronic Keying: Ensure that the electronic keying in the Logix IO configuration is set to "Compatible Keying" or "Disable Keying" if the firmware revision of the replacement unit differs from the original.
- Firmware Version Compatibility: Ensure the replacement module firmware matches or exceeds the host drive's control board firmware requirement. 20-COMM-ER cards with firmware version 2.xxx support advanced DLR features, web utility access, and modern security protocols.
Upgrade Benefits
While swapping with a refurbished 20-COMM-ER keeps the machinery running immediately, transitioning to a modern platform (such as PowerFlex 750-Series with a 20-750-ENETR) yields considerable improvements:
- DLR Network Resilience: Modern dual-port adapters provide sub-millisecond ring recovery times during a physical media break, preventing drive-trip faults on large machinery.
- Increased Parameter Bandwidth: New controller families support significantly faster DPI transmission rates and larger I/O assemblies configuration parameters.
- Enhanced Diagnostic Web Pages: Modern modules feature HTML5-based configuration pages, eliminating the need to debug outdated Java runtime environments required by legacy 20-COMM-ER web servers.
Common Migration Challenges
- IP Address Re-assignment: The 20-COMM-ER does not feature physical decimal rotary dials like modern Allen-Bradley modules. Engineering staff must use BOOTP/DHCP utility software or a 1203-USB interface with Connected Components Workbench (CCW) to configure the target IP address.
- DLR Loop Disruptions: During a hot-swap replacement within an active DLR topology, the ring will break. While the ring supervisor should keep the remaining nodes online by transitioning to a linear state, operations must be prepared for temporary network latency spikes.
- Drive DPI Fault validation: Swapping the module may trigger a
F81 DPI Port 1-6 Reference/Feedback Lossfault on the drive itself if not done under power-off conditions.
Step-by-Step Replacement Procedure
Follow these technical procedures to replace a failing 20-COMM-ER adapter safely and efficiently.
Phase 1: Preparation & Backup
- Isolate the System: De-energize the host drive. Follow company-approved Lockout/Tagout (LOTO) protocols. Wait at least 5 minutes to allow internal drive bus capacitors to fully discharge. Verify zero-voltage status at the incoming power terminals.
- Trace and Label Cables: Note which Ethernet cables are plugged into Port 1 and Port 2. In DLR topologies, maintaining the physical order of the loop is essential for diagnostic reporting.
- Document Existing Parameters: If the card is still partially accessible, use Connected Components Workbench (CCW) or the drive’s LCD HIM (Human Interface Module) to copy down the network settings:
- Parameter 3:
IP Addr Src(Value: 1 = Static parameters, 2 = DHCP, 3 = BOOTP) - Parameters 4-7:
IP Addr 1-4(The static IP address) - Parameters 8-11:
Subnet Mask 1-4 - Parameters 12-15:
Gateway Addr 1-4
- Parameter 3:
Phase 2: Physical Removal and Installation
- Unplug the Ethernet cables from the dual RJ45 ports.
- Loosen the retaining screws securing the drive cover or communication cradle.
- Carefully pull the 20-COMM-ER card away from the internal DPI connector. Be cautious not to bend the multi-pin DPI header on the host drive's main control board.
- Standard electrostatic discharge (ESD) mitigation protocols must be observed when handling the replacement board.
- Align the replacement 20-COMM-ER card with the guide pins and press the module firmly onto the DPI connector.
- Fasten the mounting screws to ensure solid chassis dynamic grounding.
Phase 3: Configuration & Commissioning
- Restore control power to the drive.
- Configure Network Parameters via HIM:
- Using the LCD HIM, navigate to:
DPI Devices->20-COMM-ER->Parameters. - Set Parameter 3 [IP Addr Src] to
1(Parameters). - Enter the target IP address in Parameters 4-7 [IP Addr 1-4].
- Enter the corresponding mask in Parameters 8-11 [Subnet Mask 1-4].
- Enter the gateway in Parameters 12-15 [Gateway Addr 1-4].
- Using the LCD HIM, navigate to:
- Navigate to Parameter 19 [Reset Module] and set it to
1(Reset Module) to apply the net parameters. The module will reboot. - Alternatively, if configuring via BOOTP/DHCP Utility:
- Boot up the Rockwell BOOTP/DHCP Server software.
- Locate the MAC address of the new 20-COMM-ER card (printed on the device label).
- Double-click the MAC address entry, assign the IP, click "Relation", and then select "Disable BOOTP/DHCP" to burn the IP configuration permanently to non-volatile memory.
- Re-insert both Ethernet cables to close the DLR loop. Verify that the LNK1 and LNK2 LED indicators turn steady green or flashing green indicating activity. Verify the MS (Module Status) and NS (Network Status) displays are solid green.
Frequently Asked Questions
Q: Can I replace a 20-COMM-ER with a standard, single-port 20-COMM-E?
A: Yes, but only if the host system does not rely on Device Level Ring (DLR) network redundancy. The 20-COMM-E only supports a single point-to-point or daisy-chain system topology. If the drive is positioned inside a DLR ring, a 1783-ETAP module must be added to route the dual-port ring down to the single-port 20-COMM-E card.
Q: Why is my PLC showing an "I/O Connection Fault" after swapping the card?
A: This is usually due to electronic keying mismatches. If the replacement card has a different firmware revision of major/minor steps (e.g., swapping a v1.002 card with a v2.001 card), the Studio 5000 controller may reject connection. Check your I/O module properties in the controller organizer and temporarily set keying to "Disable Keying" to test communications.
Q: Can I configure the IP address using the physical rotary switches on the 20-COMM-ER?
A: No. Unlike newer Rockwell network adapters, the 20-COMM-ER does not have external rotary hardware dials. Address configuration must be done programmatically using BOOTP/DHCP software or manually adjusted inside the PowerFlex HIM interface parameters.
Q: How do I resolve a "Net Dup IP" fault?
A: The "Net Dup IP" (Network Duplicate IP) diagnostic state occurs when the 20-COMM-ER detects another active machine on the network using the same IP address. Isolate the controller, ping the target IP to locate the rogue node, or re-target a unique IP address to the replacement adapter.
Related Products & Families
- 20-COMM-E: Single-port legacy EtherNet/IP adapter for PowerFlex 7-Class drives.
- 20-750-ENETR: Modern dual-port EtherNet/IP option module for PowerFlex 750-Series drives.
- 1783-ETAP: EtherNet/IP Tap module used to integrate single-port units into DLR networks.
- PowerFlex 700 / 70: The primary industrial VFD platforms utilizing the 20-COMM-ER adapter module.
Need Help?
Whether you need a drop-in replacement unit to restore system communication immediately or are planning a systematic upgrade to modern PowerFlex hardware, Palm Parts Solution can assist. We supply high-quality, fully tested new, refurbished, and surplus 20-COMM-ER units backed by a comprehensive warranty to minimize operational downtime. For pricing, availability, and technical support, contact Palm Parts Solution today.