Allen-Bradley 1770-KF2 Retrofit-Ready DH+ Interface for PLC-2 Control Systems
The Allen-Bradley 1770-KF2 is a Data Highway Plus (DH+) interface module engineered for seamless compatibility with legacy PLC-2 Series control systems. As original 1770-KF2 units reach end-of-life and factory-new stock becomes increasingly scarce, SMARTNEXMSK supplies tested, retrofit-ready replacements that allow plant engineers and system integrators to extend the operational life of existing automation infrastructure without committing to a full platform migration. Whether you are managing a brownfield retrofit, restoring a downed production line, or upgrading a control cabinet to meet current communication standards, the 1770-KF2 provides a reliable, cost-effective path forward.
The 1770-KF2 connects a host computer or programming terminal to the Data Highway Plus network, enabling real-time monitoring, program upload/download, and diagnostics across PLC-2 and compatible PLC-5 nodes. Its RS-232C serial interface bridges legacy serial communication environments to the DH+ token-passing network, making it an essential component in facilities where Allen-Bradley 1785-L40B or 1785-L80B PLC-5 controllers coexist with older PLC-2 racks on the same DH+ segment.
Upgrade Compatibility Table
| Parameter | Specification / Recommendation |
|---|---|
| Compatible Controllers | Allen-Bradley PLC-2 Series, PLC-5 Series (DH+ nodes) |
| Communication Protocol | Data Highway Plus (DH+), RS-232C serial |
| Network Baud Rate | 57.6 kbps (DH+ standard) |
| Installation Interface | RS-232C DB-25 connector to host; DH+ terminal block to network |
| Power Requirement | Supplied via host serial port or external 5 VDC; verify backplane power budget before installation |
| Replacement Recommendation | Direct drop-in for failed or obsolete 1770-KF2 units; verify firmware revision compatibility with programming software (APS, AI Series) |
| Commissioning Notes | Set node address DIP switches before power-up; confirm DH+ termination resistors at network endpoints |
| Warranty | 12-Month Warranty — covers functional defects under normal operating conditions |
Retrofit Planning for Existing Automation Systems
Successful integration of the 1770-KF2 into a legacy control environment requires a structured pre-installation audit. Begin by documenting the existing DH+ network topology: identify all active nodes, record node addresses, and confirm that the 1770-KF2 replacement will not create address conflicts with existing Allen-Bradley 1747-SDN DeviceNet Scanner modules or 1756-DHRIO ControlLogix DH+ bridge cards already on the segment.
Power budget verification is critical. The PLC-2 chassis — typically a 1771-A1B or 1771-A2B rack — must have sufficient 5 VDC backplane capacity to support the 1770-KF2 alongside installed I/O modules such as 1771-OAD AC output modules or 1771-IBD DC input modules. Overloading the 1771-P4 or 1771-P7 power supply is a common cause of intermittent communication faults during retrofit commissioning.
Terminal wiring should be mapped against the original as-built drawings. The DH+ network cable — typically Belden 9463 blue hose — must be properly terminated at both ends of the segment. If the retrofit involves extending the DH+ segment to accommodate a new 1784-PCMK or 1784-U2DHP USB-to-DH+ adapter at the engineering workstation, recalculate total cable length to remain within the 3,048-meter DH+ network limit.
For facilities migrating programming environments from the legacy APS (Advanced Programming Software) to RSLogix 500 or Studio 5000 Logview ME, the 1770-KF2 remains compatible as a communication path, provided the host PC retains a physical RS-232C port or uses a validated USB-to-serial adapter. Confirm driver compatibility with the installed version of RSLinx Classic before committing to the retrofit schedule.
Where the retrofit scope includes replacing the HMI layer — for example, retiring a PanelView 550 (2711-T5A8L1) in favor of a PanelView Plus 7 — ensure that DH+ communication tags are remapped correctly in FactoryTalk View ME before go-live. Mismatched tag addresses between the HMI and the PLC-2 program are a leading cause of extended commissioning delays in legacy upgrade projects.
Downtime Control During System Migration
Minimizing unplanned downtime during a 1770-KF2 replacement requires preparation before the maintenance window opens. Prior to shutdown, use RSLinx Classic or APS to perform a full program upload from the target PLC-2 controller and store the .RSS or .ACH file in a version-controlled backup location. Verify the backup by comparing the checksum or program revision number against the controller’s displayed value.
During the physical swap, label all DH+ network cables and RS-232C connections before disconnection. The 1770-KF2’s DIP switch settings — node address and baud rate — must be replicated exactly on the replacement unit before installation. A mismatch in node address will prevent the module from joining the DH+ token ring, resulting in communication timeouts that can appear as controller faults rather than network errors, complicating diagnosis.
After installation, power up the chassis and use RSLinx Classic’s DH+ driver configuration to verify that the replacement 1770-KF2 appears on the network at the correct node address. Perform a controlled program download and execute a full I/O force test on critical output channels before releasing the line to production. SMARTNEXMSK pre-tests all 1770-KF2 units prior to shipment to reduce on-site commissioning risk and support a target maintenance window of under four hours for a standard single-node replacement.
Retrofit Support FAQ
Q: Is the SMARTNEXMSK 1770-KF2 a direct replacement for the original Allen-Bradley unit?
A: Yes. The replacement 1770-KF2 is functionally equivalent to the original Allen-Bradley 1770-KF2 and is compatible with PLC-2 Series controllers and DH+ networks operating at 57.6 kbps. DIP switch settings for node address and baud rate must be configured to match the original unit before installation.
Q: What programming software is compatible with the 1770-KF2?
A: The 1770-KF2 is supported by Allen-Bradley APS (Advanced Programming Software) for PLC-2 programming and by RSLinx Classic as a DH+ communication driver for use with RSLogix 500 and RSLogix 5. Ensure your RSLinx Classic version supports the 1770-KF2 driver before installation.
Q: How do I verify wiring and termination before powering up?
A: Confirm that the DH+ network cable is connected to the correct terminals on the 1770-KF2 (shield, DH+ A, DH+ B) and that 82-ohm termination resistors are installed at both physical ends of the DH+ segment. Verify the RS-232C cable pinout matches the host device’s port configuration. Incorrect termination is the most common cause of DH+ communication errors after a module replacement.
Q: What does the 12-month warranty cover?
A: SMARTNEXMSK’s 12-month warranty covers functional defects in the 1770-KF2 unit under normal operating conditions, including communication failures attributable to the module itself. The warranty does not cover damage resulting from incorrect installation, overvoltage, or environmental conditions outside the module’s rated specifications. All units undergo functional testing prior to shipment.
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