20-COMM-R Remote I/O Adapter Replacement

Overview

The Allen-Bradley (Rockwell Automation) 20-COMM-R is a legacy Drive Peripheral Interface (DPI) companion module designed to interface PowerFlex 7-Class AC drives with Allen-Bradley Blue Hose Remote I/O (RIO) networks. Since its introduction, the 20-COMM-R has served as the key communications bridge for PowerFlex 70, 700, 700S, 700H, and 700L drives, enabling them to communicate with legacy programmable logic controllers like the PLC-5, SLC 500, and Logix systems equipped with scanner cards (e.g., 1756-DHRIO).

As industrial automation systems modernize, Allen-Bradley has transitioned Remote I/O networks to end-of-life (EOL) status. Finding and maintaining legacy 20-COMM-R hardware has become increasingly difficult and costly. This technical guide outlines the legacy product specifications, compatibility considerations, migration paths, and a step-by-step installation procedure for maintaining operations or upgrading your communication infrastructure.

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Legacy Product Information

The 20-COMM-R facilitates high-speed, serial communication between a host drive and a RIO network. It interfaces directly with the drive’s internal DPI port using a dedicated 20-pin ribbon cable or through an external DPI expansion kit.

Key Technical Specifications

• Protocol: Allen-Bradley Remote I/O (RIO)
• Physical Layer: 3-conductor shielded twisted-pair "Blue Hose" (Belden 9463)
• Data Rates: Supports standard RIO baud rates: 57.6 Kbps, 115.2 Kbps, and 230.4 Kbps
• Internal Drive Interface: DPI (Drive Peripheral Interface) operating up to 125 Kbps or 500 Kbps depending on the host drive model
• Addressing: Configurable via onboard physical DIP switches (Node Address 00 to 77 Octal)
• Power Requirements: Crucial operating current (150 mA at 5V DC) supplied entirely by the host drive's internal DPI bus
• Dimensions: Standard DPI communication card footprint (approx. 19mm x 86mm x 67mm)

Common Industrial Uses

• Controlling PowerFlex 700 vector-controlled drives in heavy industrial processes (water treatment, paper mills, metallurgy)
• Packaging lines relying on centralized SLC 5/04 or PLC-5 controllers
• Conveyor lines running older distributed I/O drop topologies

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Recommended Replacements

When a 20-COMM-R card fails or must be phased out, engineers can choose among several replacement paths. These range from direct "like-for-like" hardware swaps to complete network modernization.

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Compatibility Considerations

Before replacing or upgrading your 20-COMM-R, you must evaluate mechanical, electrical, and software factors.

Physical Footprint & Mounting

The 20-COMM-R is designed to fit inside the internal communication slot of PowerFlex 70 (Frame B and larger) and PowerFlex 700 drives. If you are upgrading to an Ethernet-based equivalent like the 20-COMM-E, the footprint is identical, and it will mount using the same internal standoffs. However, mechanical upgrades to newer drive lines (such as the PowerFlex 750 Series) will require physical DIN rail re-routing and cabinet space adjustments, as newer drives do not accept legacy 20-COMM-series cards without a 20-750-20COMM adapter board.

Wiring and Physical Layer

• Legacy RIO Network: Uses blue Belden 9463 twinaxial cable. It requires a terminating resistor (typically 82-Ohm or 150-Ohm, 1/2-watt) installed across the Blue and Clear conductors at the physical end-nodes of the network daisy chain.
• Modernized Ethernet: Upgrading to the 20-COMM-E requires swapping the Belden 9463 cable for shielded industrial Ethernet cabling.

Controller Logic and I/O Software Mapping

• Block Transfer Read/Write (BTR/BTW): Systems utilizing the 20-COMM-R often transfer non-real-time diagnostic parameters and configuration data via RIO block transfers.
• If you perform a direct drop-in replacement with another 20-COMM-R, you only need to ensure the DIP switches match the original.
• If you migrate to EtherNet/IP (using a 20-COMM-E), BTR/BTW logic in the PLC program must be entirely rewritten to use standard CIP Ethernet messaging (MSG instructions) or configured as Cyclic I/O assembly connections in the controller's I/O configuration tree.

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Upgrade Benefits

While swapping in a certified refurbished 20-COMM-R is the fastest way to resolve an unexpected failure, migrating to a modern industrial network protocol (such as EtherNet/IP using the 20-COMM-E or transitioning to newer PowerFlex models) offers several long-term benefits:

• Superior Diagnostic Visibility: EtherNet/IP provides deep parameter-level insights, facilitating remote troubleshooting, real-time energy monitoring, and predictive maintenance directly via a web browser or HMI.
• Simplified Cabling & Troubleshooting: Ditching legacy Blue Hose wiring in favor of standard RJ45 infrastructure eliminates frustrating grounding and impedance issues common to aging RIO daisy chains.
• Future-Proofing Integration: Eliminating legacy modules allows you to connect drive-level assets seamlessly to modern SCADA, MES, and IIoT systems.
• Reduced Spare Parts Inventory: Standardization of Ethernet components lowers storage costs, as Ethernet cables, switches, and modules are universally available.

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Common Migration Challenges

Technicians frequently encounter distinct bottlenecks when servicing or replacing RIO communication cards:

1. Forgotten Switch Settings: If the replacement adapter's onboard DIP switches are not set identically to the failed unit, the RIO Scanner will throw a "Rack Fault" or error code, causing loss of communication to all drives downstream.
2. Improper Line Termination: Accidentally leaving off the end-of-line terminating resistor (or installing the wrong value) during card replacement can corrupt waveforms, causing intermittent network drops across multiple drops.
3. Firmware Mismatches: If replacing a 20-COMM-R with a unit that has older firmware, it may not register configuration profile changes made by the host drive.
4. Incorrect RIO Coaxial Grounding: The shield of the RIO Blue Hose network must be grounded at only one end of the physical link. Dual grounding creates ground loops that cause packet drops and spurious drive faults.

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Step-by-Step Replacement Procedure

Follow this technical procedure to replace a damaged or failed 20-COMM-R adapter with a replacement unit under a direct, like-for-like swap.

Phase 1: Safety & Isolation

1. Initiate LOTO: Isolate and lock out all AC input power to the host PowerFlex drive.
2. Verify Discharge: Wait at least five minutes for the drive's internal DC bus capacitors to discharge. Verify that the DC bus voltage reads safe (<50 VDC) using a reliable digital multimeter across the drive's +DC and -DC terminals.
3. Apply ESD Protection: Equip yourself with a grounded static-safe wrist strap connected to clean chassis ground before handling any electronic modules.

Phase 2: Removal of the Defective Card

1. Open the front cover of the PowerFlex drive housing.
2. Locate the 3-pin RIO Phoenix terminal connector inserted into the front of the 20-COMM-R. Carefully pull this connector straight out of its socket. Do not cut or disconnect the individual wires from the green terminal block unless the connector itself is physically damaged.
3. Document or photograph the physical layout of the 8-position configuration DIP switch on the face of the damaged 20-COMM-R.
4. Unscrew the mounting screws securing the 20-COMM-R circuit board to the internal chassis standoffs.
5. Gently disconnect the 20-pin DPI ribbon cable connecting the adapter to the drive's internal interface board. Pull the ribbon cable connector straight back without twisting the connector pins.
6. Remove the adapter from the housing.

Phase 3: Setup & Installation of the Replacement Card

1. Place the replacement 20-COMM-R on an ESD-safe workspace.
2. Set the 8-position configuration DIP switch to match the exact pattern of the failed card.
   • Switches 1 through 6: Configures the RIO octal rack address.
   • Switches 7 and 8: Sets the RIO baud rate (57.6k, 115.2k, or 230.4k).
3. Connect the 20-pin DPI ribbon cable into the port on the rear of the replacement 20-COMM-R card. Ensure the connector key matches the slot orientation.
4. Align the communication card with the mounting standoffs inside the PowerFlex drive and secure it using the original mounting screws. Torques should be applied gently to avoid stripping plastic threads.
5. Plug the green 3-pin physical RIO Phoenix connector back into the front of the newly mounted 20-COMM-R card. Keep the shield drain wire insulation fully intact to avoid shorting against the drive housing.
6. Re-mount the drive cover and close all enclosure openings.

Phase 4: System Verification

1. Remove LOTO and restore primary power to the PowerFlex drive.
2. Observe the diagnostic status LEDs on the front face of the 20-COMM-R:
   • PORT LED: Should be steady solid Green. This indicates a valid connection to the host drive DPI interface.
   • MOD LED: Should be steady solid Green, indicating active and functional module status.
   • NET LED: Steady solid Green indicates that the RIO Scanner has established active network communication with the card and cyclical mapping is active.
3. If any LEDs flash orange or red, consult the fault-finding lookup table in the 20-COMM-R manual to trace node addressing or cabling mismatches.

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Frequently Asked Questions (FAQs)

Q1: The PORT LED on my replacement 20-COMM-R is flashing Green. What does this mean?

A flashing Green PORT LED indicates that the communication adapter is functioning correctly, but a logical connection has not yet been initiated by the host drive. Power cycle the drive to force a fresh DPI register handshake. If the issue persists, check that the host drive’s DPI speed and configuration parameters correspond with the adapter's capabilities.

Q2: Can a 20-COMM-E card be used to drop-in replace a 20-COMM-R card on a RIO network?

No, the 20-COMM-E communicates exclusively over the EtherNet/IP protocol. It cannot physically interface with or translate signals to a legacy RIO Blue Hose network without a protocol-specific external network translator, such as a ProSoft AN-X2 gateway.

Q3: How do I choose between an 82-Ohm and a 150-Ohm terminating resistor for the RIO network?

The resistor value is dictated by your system's transmission configuration. Standard-rate Remote I/O configurations running at 57.6 Kbps or 115.2 Kbps with typical Belden 9463 cable require a 150-Ohm resistor across terminating pins. If running at the maximum rate of 230.4 Kbps (or using high-output scanner modules configured for 82-Ohm impedance), use an 82-Ohm resistor.

Q4: My replacement card isn’t communicating, and the MOD LED is flashing Red. Is it dead on arrival?

A flashing Red MOD LED usually indicates a non-volatile check-sum configuration error or a mismatch between the card's stored drive profile and the actual physical drive model. You may need to perform a factory reset of the adapter parameters using a HIM (Human Interface Module) or Connected Components Workbench (CCW) software, then reinitialize the drive parameters.

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Related Products & Families

To complete your legacy infrastructure maintenance or plan an upgrade, you may require related Rockwell and Allen-Bradley drives, networks, and components:

• PowerFlex 70 and 700 AC Motors Drives: The definitive legacy hardware hosts for the 20-COMM-R.
• 1756-DHRIO Module: The primary ControlLogix Remote I/O and DH+ scanner card bridging older drops with modern Logix architectures.
• 1747-SN Sub-module: The legacy SLC 500 scanner card responsible for addressing RIO drops.
• 20-COMM-E / 20-COMM-C / 20-COMM-D: Auxiliary communication adapter modules for EtherNet/IP, ControlNet, and DeviceNet, respectively.
• Belden 9463 Blue Hose: The physical media cable standard for rugged industrial RIO networks.

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Need Help?

Finding and configuring obsolete hardware like the 20-COMM-R can be challenging when production is on the line. At Palm Parts Solution, we specialize in keeping legacy control systems running smoothly. We can supply you with new, high-quality refurbished, or hard-to-find surplus 20-COMM-R adapters—all fully tested and backed by a comprehensive warranty. If you are experiencing drive communication issues, contact our technical team today to source the parts you need to restore your operations.