Allen-Bradley 1770-KFD PLC Communication Module – 1770 Series

Allen-Bradley 1770-KFD: DH+ to RS-232 Protocol Bridge in Distributed Control Architectures

The Allen-Bradley 1770-KFD functions as a dedicated protocol conversion node between Data Highway Plus (DH+) token-passing networks and RS-232 serial interfaces. In a distributed PLC environment, this module occupies a critical position: it decouples the programming workstation or HMI from the DH+ bus without consuming a backplane slot, preserving rack capacity for I/O and specialty modules. Its external desktop form factor allows placement at the network boundary, where RS-232 signal integrity is maintained over short cable runs while DH+ handles the deterministic token-passing across the plant floor network.

Within a control loop, the 1770-KFD serves as the diagnostic and programming gateway. Maintenance engineers connect a laptop via DB-9 RS-232 to upload/download ladder logic, monitor data table values, and execute forced I/O operations on PLC-5, SLC 500, and MicroLogix platforms — all without interrupting live production traffic on the DH+ segment. The module’s internal microcontroller manages baud rate negotiation on the RS-232 side while synchronizing to the DH+ token rotation on the network side, providing transparent bidirectional data flow at sustained throughput rates compatible with RSLinx Classic KF driver architecture.

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Technical Parameters

Hardware Logical Analysis

The 1770-KFD’s internal architecture centers on a dual-port communication controller that manages two physically and electrically independent data paths simultaneously. On the DH+ side, the module implements the full token-passing MAC layer: it monitors the token rotation, requests the token when a frame is queued for transmission, and releases it within the protocol-defined window. This prevents the module from introducing latency jitter into the DH+ network — a critical requirement in time-sensitive PLC scan cycles where DH+ polling must complete within deterministic bounds.

On the RS-232 side, the module implements hardware flow control via RTS/CTS handshaking, preventing buffer overrun when the host PC’s serial driver cannot service incoming data fast enough. The internal FIFO buffer absorbs burst traffic from the DH+ side and presents it to the RS-232 port at a rate the host can process, decoupling the two clock domains without data loss.

From an EMC standpoint, the 1770-KFD’s external enclosure provides a degree of shielding isolation between the RS-232 cable (which can act as an antenna in electrically noisy industrial environments) and the DH+ network wiring. The RS-232 port’s inherent single-ended signaling is kept physically short — typically under 15 m — while DH+ uses differential signaling over shielded twisted-pair, providing common-mode noise rejection across longer cable runs up to 3,048 m at reduced baud rates. This architectural separation means that electrical disturbances on the RS-232 side (e.g., from nearby VFDs or welding equipment) do not propagate onto the DH+ bus and corrupt network traffic.

The DIP switch-based node address configuration eliminates firmware dependency for basic setup, reducing commissioning time and eliminating the risk of address conflicts caused by software misconfiguration. Each node address is latched at power-up, ensuring stable network participation even after power cycling events common in industrial environments.

System Integration Benefits

• Zero backplane slot consumption: The external form factor preserves all rack slots for I/O, specialty, and communication modules, maximizing the functional density of existing PLC-5 and SLC 500 racks without hardware expansion.
• Deterministic DH+ participation: Full token-passing MAC implementation ensures the module participates in the DH+ network without disrupting the token rotation timing, maintaining scan cycle predictability for all other nodes on the segment.
• Transparent RSLinx driver compatibility: The KF driver in RSLinx Classic communicates with the 1770-KFD using the same protocol framing as rack-mounted DH+ cards, allowing existing RSLogix 500 and RSLogix 5 projects to connect without driver reconfiguration.
• Dual baud rate independence: RS-232 and DH+ baud rates are configured independently, allowing the host PC to operate at its optimal serial speed while the DH+ network runs at its installed baud rate — no forced compromise between the two interfaces.
• Non-intrusive diagnostics: Engineers can monitor live data table values, force I/O states, and capture communication traffic without placing the PLC in program mode, supporting online diagnostics during production without process interruption.
• Legacy system longevity: For plants operating PLC-5 or SLC 500 systems beyond their original design life, the 1770-KFD extends the useful service life of the DH+ infrastructure by maintaining a viable programming and monitoring interface compatible with current PC hardware.
• Simplified cable management: A single RS-232 cable from the workstation to the 1770-KFD, combined with the existing DH+ trunk cable, eliminates the need for dedicated communication cards in the programming PC — reducing hardware cost and cable routing complexity at the panel.
• Fault isolation at the network boundary: Because the 1770-KFD is an external node rather than a backplane-mounted card, a failure in the RS-232 interface or the module itself does not affect PLC operation or DH+ network continuity. The PLC continues executing its control program; only the programming/monitoring connection is interrupted.

Quality Assurance & Global Logistics

Every 1770-KFD unit supplied by siemensplc.com is sourced as genuine Allen-Bradley hardware manufactured by Rockwell Automation. Units are procured through verified industrial surplus and authorized secondary-market channels, with source documentation retained for traceability. Prior to shipment, each module undergoes physical inspection covering connector condition, label authenticity, housing integrity, and serial number cross-reference against known OEM production records.

Functional verification includes power-on confirmation and, where test fixtures are available, DH+ communication handshake testing to validate the module’s network participation logic before packaging. Units that do not pass inspection are quarantined and not shipped.

Logistics operations are based in Xiamen, China, with established carrier partnerships covering express air freight (DHL, FedEx, UPS) and economy air options for cost-sensitive shipments. Standard in-stock orders are dispatched within 1–3 business days. Export documentation — commercial invoice, packing list, and certificate of origin — is prepared as standard for all international shipments. Anti-static ESD packaging with foam cushioning is used for all electronic modules. For orders requiring expedited customs clearance or specific HS code documentation, our logistics team provides pre-shipment coordination upon request.

All units are covered by a 12-month warranty from the date of shipment, covering defects in materials and workmanship under normal operating conditions.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
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