20-COMM-D DeviceNet Adapter Replacement Guide

Overview

In modern industrial automation, legacy fieldbus networks like DeviceNet are steadily being phased out in favor of high-speed Industrial Ethernet solutions. The Allen-Bradley PowerFlex 20-COMM-D DeviceNet Adapter has served as a core interface for connecting PowerFlex 7-Class AC drives to DeviceNet networks for decades. However, with the product line currently in its obsolescence phase, legacy spare parts are becoming harder to source, and plant managers must plan for seamless replacements or direct migrations.

This guide provides a comprehensive overview of the 20-COMM-D module, outlines viable direct replacements and migration paths, and offers a step-by-step replacement procedure to minimize system downtime.

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Legacy Product Information

The 20-COMM-D is a Drive Peripheral Interface (DPI) to DeviceNet communication adapter designed specifically for integrated installation inside legacy PowerFlex 7-Class drives.

Key Technical Specifications

• Catalog Number: 20-COMM-D
• Network Protocol: DeviceNet (Standard 5-pin open-style linear connector)
• Drive Interface: DPI (Drive Peripheral Interface)
• Data Transfer Rates: 125 kbps, 250 kbps, and 500 kbps (Autobaud capability supported)
• Maximum Node Capacity: 64 nodes (MAC ID: 0 to 63)
• Current Draw (Network DeviceNet): 60 mA at 24V DC
• Current Draw (Drive DPI): 150 mA at 5V DC
• Status Indicators: Four diagnostic LEDs (PORT, MOD, NET A, NET B)

Lifecycle Status & Common Uses

The 20-COMM-D adapter is classified as End of Life (EOL) / Obsolete by Rockwell Automation. It was primarily used to integrate PowerFlex 70, 700, 700S, 700H, and 700S AC drives into Allen-Bradley SLC 500, PLC-5, and ControlLogix control systems via DeviceNet scanner modules (such as the 1756-DNB or 1769-SDN).

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Recommended Replacements

When a 20-COMM-D module fails, maintenance teams have three distinct pathways: sourcing a direct replacement unit, migrating to a modernized EtherNet/IP network, or upgrading the entire drive platform.

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Compatibility Considerations

Hardware & Footprint

The 20-COMM-D features an internal mounting design that slides directly into the drive’s communication slot and secures using a unique retaining screw. If migrating to the 20-COMM-E (EtherNet/IP), the adapter physical footprint and mounting styles are identical, meaning no custom cabinet fabrication or external dynamic enclosures are required. However, the physical network medium changes from 5-pin DeviceNet cabling to standard RJ45 shielded Ethernet Patch Cables (Cat 5e or higher).

Firmware & Drive Compatibility

The 20-COMM-D is compatible with any drive utilizing the DPI protocol, including:

• PowerFlex 70 (all phases)
• PowerFlex 700 (Vector Control and Standard Control)
• PowerFlex 700H, 700S, and 753 (via 20-750-20COMM carrier card)

If migrating to the 20-COMM-E, check the firmware compatibility of the drive's main control board to ensure it supports Parameter-to-I/O configuration mapping over EtherNet/IP.

Software Configuration

Replacing a 20-COMM-D with another 20-COMM-D requires configuring the Node Address (MAC ID) and Baud Rate to match the original unit. This is done via physical rotary switches on the module or through configuration software.

If transitioning to 20-COMM-E, you must remove the node from the DeviceNet scanlist in RSNetWorx for DeviceNet and configure it under the Ethernet bridge module tree in RSLogix 5000 / Studio 5000.

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Upgrade Benefits

While swapping in a surplus 20-COMM-D is the fastest immediate fix, migrating to an EtherNet/IP platform such as the 20-COMM-E or a newer PowerFlex 750-Series drive offers significant operational advantages:

1. Enhanced Diagnostic Capabilities: EtherNet/IP provides significantly higher bandwidth, allowing real-time retrieval of drive diagnostics, advanced parameters, and environmental metrics.
2. Simplified Integration: EtherNet/IP integrates seamlessly within the Studio 5000 environment using Add-On Profiles (AOPs), removing the need for RSNetWorx configuration and manual I/O mapping.
3. Reduced Tooling Dependency: Traditional DeviceNet requires specialized software (RSNetWorx) and communications interfaces (such as the 1784-U2DN). Ethernet settings can be adjusted using standard web browsers and standard network switches.
4. Network Longevity: Ethernet components have a much longer support lifecycle, minimizing the risk of downtime due to component scarcity.

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Common Migration Challenges

• Address Mapping Conflicts: DeviceNet uses physical node addressing (MAC IDs 0–63). During replacement, if the rotary switches do not match the old unit's hardware address, direct communication with the Master Scanner will fail.
• Network Power Overhead: DeviceNet relies on external 24V DC network power (usually provided by a dedicated power supply). Ensure this 24V supply remains stable (ideally within 11-25V DC range) to prevent node dropout.
• EDS File Synchronization: If the replacement 20-COMM-D contains a different firmware revision, RSNetWorx or the PLC may throw an "Electronic Keying" fault. You must register the correct Electronic Data Sheet (EDS) file in the RSLinx system.
• PLC Scanlist Re-configuration: In physical swaps of identical parts, simply downloading the parameters is sufficient. In protocol migrations, the scanner scanlist must be updated inside the controller program, which requires putting the PLC into Program or Offline mode.

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Step-by-Step Replacement Procedure

Follow these technical instructions to replace an active 20-COMM-D DeviceNet module.

Step 1: Safety & Power Isolation

1. Safely stop the drive and connected machinery.
2. Perform standard Lockout/Tagout (LOTO) procedures.
3. Turn off primary AC input power to the PowerFlex drive.
4. Turn off external 24V DC DeviceNet network power (if dedicated).
5. Wait at least 5 minutes to allow the drive's internal DC bus capacitors to fully discharge. Use a reliable digital multimeter to verify that voltage on the DC bus correlates to 0V.

Step 2: Extracting the Legacy Module

1. Unscrew the cover retention screws of the PowerFlex drive to access the internal control cabinet structure.
2. Disconnect the 5-pin open-style DeviceNet terminal plug from the bottom of the 20-COMM-D.
3. Loosen the module’s retaining screw located at the top-left section of the communication card.
4. Gently pull the 20-COMM-D forward to disconnect it from the drive's internal DPI ribbon cable or main system board interface.

Step 3: Configuring the Replacement Module

Before inserting the new or refurbished 20-COMM-D, copy the configuration of the old unit:

1. Locate the physical rotary switches on the replacement module.
2. Set the MAC ID (0 to 63) to match the previous module's configuration. Note: If using software configuration, set the switches to 99.
3. Locate the slide switches or jumper pins for the DeviceNet baud rate configuration (set to match either 125k, 250k, 500k, or Multi-Drive/Autobaud).

Step 4: Physical Installation

1. Align the 20-COMM-D pin headers with the drive’s DPI slot.
2. Carefully push the module in place until the internal card-edge or ribbon connectors are securely seated.
3. Tighten the retaining screw to lock the module in place. Do not over-torque.
4. Re-attach the 5-pin DeviceNet terminal plug. Confirm the wire routing matches standard color conventions:
   • Red: V+
   • White: CAN_H
   • Bare: Shield
   • Blue: CAN_L
   • Black: V-

Step 5: Power-Up and Commissioning

1. Re-apply 24V DC network power and AC input power to the drive.
2. Observe the onboard status LEDs:
   • PORT LED: Should display solid Green inside 10 seconds, indicating stable DPI communication with the drive.
   • MOD LED: Solid Green, indicating the adapter is operating normally.
   • NET A LED: Solid Green, indicating that the module is online and has active connections established with the Scanner.
3. Run RSNetWorx for DeviceNet to upload the network profile. Verify the replacement module shows no configuration conflicts.
4. Test basic drive commands (Start, Stop, and Speed Reference) to verify network traffic is flowing correctly.

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Frequently Asked Questions

Q1: What do the different flashing states of the "NET A" LED mean?

• Off: The module is not online, or 24V DC DeviceNet network power is missing.
• Flashing Green: The module is online and operating at the correct baud rate, but no explicit connection has been established configuration-wise (is and remains idle).
• Solid Green: Ready and active. The module is online and has an established I/O connection in the active state.
• Flashing Red: One or more I/O connections have timed out.
• Solid Red: Critical communication failure. The node has a duplicate MAC ID address or is suffering from bus-off errors.

Q2: Can I hot-swap the 20-COMM-D card while the drive is powered?

No. Removing or inserting a 20-COMM-D card while the PowerFlex drive control power is energized can damage the internal DPI interface connector, the communication card itself, and the drive's main control board. Always isolate all power before servicing.

Q3: My PLC is throwing an Electronic Keying Mismatch error after replacement. How do I fix this?

This occurs when the replacement 20-COMM-D module has a different major/minor firmware version than the original unit configuration registered in Logix. To resolve this, download the matching EDS file from Rockwell Automation's database, register it using the EDS Wizard, and update the module definition in Studio 5000 (or change the Keying configuration to "Compatible Module" or "Disable Keying").

Q4: Can I use the 20-COMM-D on a PowerFlex 40 or 400 drive?

No. PowerFlex 4-Class drives utilize DSI (Drive Serial Interface) protocol rather than DPI. For DeviceNet on PowerFlex 40/400 drives, you must use a 22-COMM-D module instead.

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Related Products & Families

To complete your upgrade or replace connected components alongside your 20-COMM-D, consider the following associated product families:

• Allen-Bradley PowerFlex 70 / 700 AC Drives: Industrial heavy-duty variable frequency drives.
• 20-COMM-E / 20-COMM-ER: EtherNet/IP alternative communication modules for legacy 7-Class drives.
• 1756-DNB ControlLogix / 1769-SDN CompactLogix: DeviceNet Master Scanner Modules.
• 20-750-DNTP / 20-750-DNET: Network integration cards for upgrading to PowerFlex 750 series drives.

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Need Help?

Whether you need to quickly locate an identical, reliable 20-COMM-D module or map out an institutional migration path to EtherNet/IP, Palm Parts Solution has you covered. We can supply new, high-quality refurbished, or reliable surplus industrial automation parts with a comprehensive warranty program to keep your facility run times resilient and efficient. Contact our technical support team today for part availability, hardware compatibility questions, or specialized component sourcing.