Allen-Bradley 1770-KFD Retrofit-Ready DH+ Interface for 1770 Series Control Systems
The Allen-Bradley 1770-KFD is a Data Highway Plus (DH+) to RS-232 communication interface designed to bridge legacy PLC-5 and SLC 500 control platforms with modern programming environments and SCADA systems. As a retrofit-ready replacement for discontinued or aging communication links, the 1770-KFD remains one of the most sought-after interface modules for engineers managing older Allen-Bradley control architectures. Whether you are restoring a failed communication link, upgrading a control cabinet, or migrating from a legacy DH+ network to a more maintainable topology, this module provides a reliable, drop-in solution backed by a 12-month warranty and pre-shipment functional testing.
Upgrade Compatibility Table
| Parameter | Details |
|---|---|
| Compatible Platforms | PLC-5 Series, SLC 500 Series, MicroLogix (via DH+ adapter) |
| Communication Protocol | DH+ (Data Highway Plus) ↔ RS-232C |
| Interface Connector | DB-9 RS-232 (PC side); DH+ terminal block (PLC side) |
| Baud Rate Support | 57.6 kbps / 115.2 kbps (DH+ selectable) |
| Installation Requirement | DIN rail or panel mount; no backplane slot required |
| Replacement Compatibility | Direct replacement for 1770-KFD, 1770-KFD2 (verify firmware revision) |
| Programming Software | RSLogix 5, RSLogix 500, RSLinx Classic |
| Commissioning Note | Set node address via DIP switch; verify RSLinx driver configuration |
| Warranty | 12-Month Warranty — functional test included before shipment |
Retrofit Planning for Existing Automation Systems
Replacing a failed or end-of-life 1770-KFD in an active production environment requires careful pre-planning to avoid extended downtime. Before removing the existing module, document the current DH+ node address (typically set via DIP switches on the module body), the RS-232 cable pinout connecting to the programming terminal or SCADA workstation, and the RSLinx Classic driver configuration including the COM port assignment and baud rate.
In many retrofit scenarios, the 1770-KFD serves as the sole communication path between the PLC-5 processor — such as a 1785-L40B or 1785-L80B — and the RSLogix 5 programming workstation. Loss of this link means loss of online monitoring, program upload capability, and fault diagnostics. Engineers should prepare an offline backup of the PLC-5 program using RSLogix 5 before beginning any hardware swap.
For control cabinets that also house a 1746-A13 SLC 500 chassis with modules such as the 1746-IB16 digital input card, 1746-OB16 digital output card, or 1746-NI4 analog input module, the DH+ network topology must be verified to ensure the 1770-KFD node address does not conflict with existing SLC 5/04 or SLC 5/05 processors on the same DH+ segment. Node addresses must be unique across all devices on the network.
Where the retrofit also involves upgrading the HMI layer — for example, replacing a legacy PanelView 550 or PanelView 900 terminal with a PanelView Plus 7 — the DH+ communication link supported by the 1770-KFD may need to be extended or bridged using a 1761-NET-AIC or a 1784-PKTX card, depending on the new HMI’s communication capabilities. Confirm that the HMI tag database and screen logic are compatible with the existing PLC-5 data table structure before finalizing the migration plan.
Power supply capacity is another critical checkpoint. The 1771 I/O chassis power supply — such as the 1771-P4S or 1771-P7 — must have sufficient reserve capacity to support any additional modules introduced during the upgrade. Similarly, if the retrofit involves adding a 1756-DHRIO ControlLogix bridge module to extend DH+ connectivity into a newer ControlLogix platform, the 1756-A7 or 1756-A10 chassis power budget must be reviewed.
All replacement modules supplied by SMARTNEXMSK undergo functional testing prior to shipment. In-stock inventory ensures rapid dispatch, and the 12-month warranty covers both hardware defects and communication failures identified during commissioning.
Downtime Control During System Migration
Minimizing unplanned downtime during a DH+ communication retrofit begins with a structured changeover plan. The recommended approach is to perform the physical module swap during a scheduled maintenance window, with the PLC processor placed in Program mode rather than Run mode to prevent unintended output activation during the transition.
Before powering down the cabinet, use RSLinx Classic to verify the current DH+ network status and confirm all nodes are communicating normally. Take a screenshot or export the RSLinx driver configuration so it can be restored exactly on the replacement module. If the existing 1770-KFD is connected to a 1785-L40B PLC-5 processor, upload the current ladder logic program to RSLogix 5 and save a timestamped backup to a secure location.
After installing the replacement 1770-KFD, set the DIP switches to match the original node address, reconnect the RS-232 cable, and restore the RSLinx Classic driver configuration. Power up the cabinet and verify that RSLinx detects the DH+ network and all expected nodes before returning the processor to Run mode. For systems with a PanelView HMI on the DH+ network, confirm that the HMI communication link is re-established and that all screen navigation and data display functions are operating correctly before releasing the line to production.
In cases where the 1770-KFD is being replaced as part of a broader migration from PLC-5 to ControlLogix, the 1756-DHRIO module can be used to maintain DH+ connectivity during a phased cutover, allowing the legacy PLC-5 and the new ControlLogix system to coexist on the same DH+ segment until the migration is complete. This approach preserves original program logic and HMI screen functionality throughout the transition, reducing the risk of production disruption.
Retrofit Support FAQ
Q1: Is the 1770-KFD a direct drop-in replacement for the 1770-KFD2?
In most applications, yes. Both modules perform the same DH+ to RS-232 bridging function. However, the 1770-KFD2 introduced minor firmware revisions affecting baud rate negotiation with certain RSLinx versions. Verify your RSLinx Classic version and DH+ baud rate setting before installation. Our technical team can assist with compatibility confirmation prior to shipment.
Q2: What wiring changes are required when replacing the 1770-KFD?
The DH+ terminal connections (Shield, DH+ A, DH+ B) and the RS-232 DB-9 connector pinout are identical between revisions. No wiring changes are typically required. Confirm the DIP switch node address setting matches the original module before powering up.
Q3: How is the module tested before shipment?
Each 1770-KFD unit is powered up and tested for DH+ communication link establishment and RS-232 data transmission prior to dispatch. A functional test report is available upon request. All units are covered by a 12-month warranty from the date of shipment.
Q4: Can this module be used with RSLogix 5000 and ControlLogix systems?
The 1770-KFD is designed for DH+ networks connected to PLC-5 and SLC 500 platforms. For ControlLogix integration, the 1756-DHRIO module is the recommended bridge. However, the 1770-KFD can still be used as a programming interface for legacy PLC-5 processors operating alongside a ControlLogix system during a phased migration.
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