Allen-Bradley 1770-KFD Replacement for DH+ RS-232 Series

Product Overview

Allen-Bradley 1770-KFD Replacement for DH+ RS-232 Series: Seamless Migration from Legacy PLC Communication Systems

The Allen-Bradley 1770-KFD is a DH+ to RS-232 communication interface module widely deployed in legacy Rockwell Automation control architectures. As this model reaches end-of-life and becomes increasingly difficult to source through standard distribution channels, many industrial facilities face urgent decisions: repair, replace, or migrate. TOPNLMS supplies verified 1770-KFD replacement units and compatible upgrade solutions designed to minimize downtime, preserve existing wiring infrastructure, and maintain communication continuity across your control network.

Whether you are maintaining an aging Data Highway Plus (DH+) network or planning a phased migration to a modern Ethernet-based architecture, the 1770-KFD replacement path offered by TOPNLMS provides a technically sound, cost-effective bridge between legacy and current-generation Allen-Bradley systems.

Compatibility Comparison Table

Seamless Upgrade Solutions

Replacing the 1770-KFD is rarely an isolated task. In most retrofit and migration projects, the communication interface sits at the center of a broader system that includes multiple interdependent components. Understanding the full upgrade path helps procurement teams and system integrators plan accurately and avoid secondary failures during commissioning.

In a typical DH+ network running Allen-Bradley PLC-5 or SLC 500 controllers, the 1770-KFD serves as the programming and SCADA communication bridge between the RS-232 port of a host PC running RSLinx Classic and the DH+ network backbone. When this interface fails or becomes unavailable, the entire programming and monitoring capability of the network is interrupted. Replacing the 1770-KFD restores this link without requiring changes to the PLC-5 processor, the 1771 I/O chassis, or the existing DH+ trunk cable.

For facilities running SLC 500 systems, the 1747-L553 or 1747-L552 processor modules communicate natively over DH+, and the 1770-KFD replacement restores full RSLogix 500 programming access without any ladder logic modification. Similarly, MicroLogix 1000 and MicroLogix 1100 controllers with DH+ capability benefit directly from this replacement without requiring changes to the 1762 expansion I/O modules already installed in the panel.

In more complex migration scenarios — for example, transitioning from a PLC-5 platform toward a ControlLogix or CompactLogix architecture — the 1770-KFD replacement serves as a temporary but critical bridge during the transition period. During this phase, engineers often need simultaneous access to both the legacy DH+ network and the new EtherNet/IP backbone. The 1756-DHRIO communication module installed in a ControlLogix 1756 chassis can bridge DH+ to the new Logix platform, while the 1770-KFD continues to provide direct RS-232 access for legacy programming tasks. This dual-access approach reduces migration risk and allows phased cutover without full system shutdown.

Panel-level components that commonly accompany a 1770-KFD replacement project include the 1756-PA72 or 1756-PB72 power supply modules for ControlLogix chassis, 1492 terminal block assemblies for signal rewiring, and 1585 Ethernet patch cables for new network segments. Where signal isolation is required between the RS-232 host and the DH+ network — particularly in electrically noisy environments — a DIN-rail mounted signal isolator or RS-232 surge protector is recommended as part of the installation.

For facilities that also need to upgrade their HMI layer during the same maintenance window, PanelView Plus 7 terminals with EtherNet/IP connectivity can be commissioned in parallel with the 1770-KFD replacement, allowing operators to maintain visibility into the legacy DH+ network while the new HMI infrastructure is validated.

Retrofit Guidance FAQ

Q: Will the replacement 1770-KFD work with RSLinx Classic without driver reconfiguration?
A: Yes. The replacement unit is electrically and functionally equivalent to the original. RSLinx Classic will detect it on the same COM port using the existing 1770-KFD driver. No driver reinstallation or reconfiguration is required in most cases.

Q: Does replacing the 1770-KFD require any changes to the PLC program?
A: No. The 1770-KFD is a passive communication interface and does not affect the PLC program stored in the processor. Replacing the unit has no impact on ladder logic, data tables, or I/O configuration in PLC-5 or SLC 500 systems.

Q: Is the replacement unit compatible with both DH+ and DH-485 networks?
A: The 1770-KFD is specifically designed for DH+ networks. For DH-485 communication (used with SLC 500 and MicroLogix via the 1747-PIC or AIC+ modules), a different interface is required. Please confirm your network type before ordering.

Q: What cable is required between the 1770-KFD and the host PC?
A: A standard RS-232 null modem or straight-through cable (DB-9 male to DB-9 female) is used depending on the host port configuration. Most installations use a straight-through cable. Cable length should be kept under 15 meters to maintain signal integrity.

Q: Can the 1770-KFD replacement be used in a panel with limited space?
A: Yes. The 1770-KFD does not occupy a rack slot and requires only a cable connection to the DH+ network and the RS-232 host. It can be mounted externally or stored in the cable management area of the control cabinet without any structural modification.

Q: What happens if the DH+ network baud rate is mismatched?
A: The DH+ baud rate must match across all nodes on the network. The 1770-KFD supports 57.6 kbps, which is the standard DH+ rate. Verify the baud rate setting on the PLC processor and all other DH+ nodes before commissioning the replacement unit.

Warranty Assurance

Every 1770-KFD replacement unit shipped by TOPNLMS is covered by a 12-month warranty from the date of delivery. Prior to shipment, each unit undergoes functional verification including communication protocol testing, RS-232 signal integrity checks, and visual inspection for physical damage. Units that do not pass verification are not shipped.

In the event of a warranty claim, TOPNLMS provides replacement unit dispatch within 3 business days of confirmed fault diagnosis. Our technical support team is available to assist with installation questions, RSLinx driver configuration, and network commissioning via email and phone during business hours (UTC+8).

For procurement teams managing critical infrastructure, TOPNLMS maintains buffer stock of high-demand legacy communication interfaces to support emergency replacement orders. Express shipping options are available to most destinations, with standard lead times of 3–7 business days for international orders.

All units are shipped with anti-static packaging, individual serial tracking, and a printed test certificate. Customs documentation including commercial invoice, packing list, and HS code declaration is provided for all international shipments.