Allen-Bradley 1756-CP3​ ControlLogix / SLC 500 RS-232 Programming Cable – 3 m (9.8 ft) DB9 Female to Right-Angle DB9 Female for DF1 / DH-485 Communication

Product Overview

The Allen-Bradley 1756-CP3​ is a 3-meter (9.8 ft) RS-232 serial communication cable specifically designed by Rockwell Automation for local point-to-point connection between a personal computer (or programming terminal with a DB9 serial port) and the serial programming port (Channel 0) of ControlLogix® 5550-series processors (such as the 1756-L55x), as well as SLC 500 processors equipped with a DB9 RS-232 port (SLC 5/03, 5/04, and certain 5/05 configurations using DF1 or DH-485 via RS-232). One end of the 1756-CP3​ terminates in a right-angle DB9 female connector that plugs directly into the processor’s serial port—its low-profile 90-degree orientation preventing strain on the PLC port and allowing adjacent modules or cables to fit without obstruction in a densely populated control cabinet. The opposite end is a straight DB9 female connector intended for the PC’s COM port or a USB-to-DB9 serial adapter.The Allen-Bradley 1756-CP3​ incorporates the correct null-modem (crossover) pinout required for DF1 Full-Duplex protocol communication between a DTE (PC) and DTE (PLC processor), eliminating the need for users to source or build custom cross-wired serial cables. It is fully compatible with Rockwell Software® RSLogix 500™, RSLogix 5000™ (for legacy online monitoring via serial), RSLinx® Classic, and other DF1-capable configuration tools. While modern laptops often lack native DB9 serial ports, the 1756-CP3​ remains an essential field-service accessory when used in conjunction with a qualified industrial USB-to-RS232 adapter, providing the reliable, noise-tolerant local connection needed for initial project downloads, firmware updates (via ControlFLASH), offline-to-online compares, and troubleshooting when Ethernet access to the controller is unavailable or impractical.As a genuine Rockwell Automation cable, the 1756-CP3​ is constructed with shielded twisted-pair conductors and molded strain-relief boots to withstand repeated flexing and the rigors of shop-floor use. It is the recommended standard programming cable for any service technician maintaining ControlLogix or SLC 500 systems that require direct serial access, and it is typically stocked as a spare in automation maintenance cribs to avoid project delays caused by missing or incompatible third-party serial cables.

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Description

 

Technical Specifications

Product Model | 1756-CP3Manufacturer | Allen-Bradley / Rockwell AutomationProduct Type | RS-232 Serial Programming / Configuration Cable for ControlLogix & SLC 500 ProcessorsCable Length | 3.0 m (118 in / 9.8 ft)Connector A (PLC Side) | DB9 Female, Right-Angle (90°) — plugs into Processor Channel 0 RS-232 portConnector B (PC Side) | DB9 Female, Straight — plugs into PC COM port or USB-Serial AdapterPinout Configuration | Null-Modem (Crossover) — TXD/RXD crossed, DSR/DTR/CD handshake lines appropriately wired for DF1 Full-Duplex DTE↔DTESupported Protocols | DF1 Full-Duplex (Point-to-Point), DH-485 (when processor port configured for RS-232 DH-485), ASCII modeBaud Rate Support | 110 bps to 115.2 kbps (limited by processor port capability; typical use 19.2 kbps or 38.4 kbps for programming)Conductor Type | Shielded Twisted Pair (STP) with overall foil shield, drain wire terminated at molded connector shellsOperating Temperature (Cable) | -20 °C to +60 °C (-4 °F to +140 °F)Compatibility | ControlLogix 1756-L1, 1756-L55x (Channel 0 RS-232); SLC 500 1747-L532, L542, L543, L551, L552, L553, L554 (DF1 RS-232 on Channel 0); PanelView terminals with DB9 RS-232 config port (select models)Certifications | RoHS Compliant, CE Marked (as part of Rockwell Automation accessory line)Replaces / Supersedes | Earlier 1747-CP3 in most SLC 500 serial applications; 1756-CP3 is the current catalog number for this cable configuration

Main Features and Advantages

Right-angle PLC-side connector for space-saving installation: The defining physical advantage of the 1756-CP3​ is its right-angle DB9 female connector on the processor end. In a ControlLogix or SLC 500 chassis mounted in a shallow enclosure, a straight-back DB9 plug can foul adjacent modules or the cabinet door. The 90-degree orientation routes the cable parallel to the chassis face, preserving clearance and reducing mechanical stress on both the cable boot and the processor’s serial port receptacle—particularly important during repeated connect/disconnect cycles in the field.Correct DF1 null-modem pinout, verified and guaranteed: Many generic DB9 serial cables are straight-through (modem / DCE-DTE) and will NOT establish communication with a Rockwell Automation processor’s Channel 0. The 1756-CP3​ is factory-wired with the precise crossover needed for DTE-to-DTE DF1 Full-Duplex communication—TXD (Pin 3 ↔ Pin 2), with RTS/CTS and DSR/DTR/CD appropriately looped—so technicians get a reliable link on the first attempt without guesswork or custom wiring diagrams. This eliminates one of the most common causes of “cannot go online” errors during commissioning.Shielded industrial-grade construction: Unlike inexpensive off-the-shelf null-modem cables, the 1756-CP3​ uses individually shielded twisted pairs with an overall foil shield drained to the metal-shell DB9 connectors, providing improved immunity to electrical noise in electrically harsh plant environments. Molded strain reliefs at both ends resist kinking and pull-out, and the cable jacket is formulated for flexibility during cold-weather winter commissioning as well as resistance to oils and common industrial contaminants encountered in maintenance shops.Universal Rockwell software compatibility: The 1756-CP3​ works transparently with RSLinx Classic (auto-detects DF1 driver at the configured COM port), RSLogix 500 (SLC 500 uploads/downloads and online monitoring), RSLogix 5000 / Studio 5000 (serial online viewing and initial download to a new ControlLogix L55 processor before Ethernet is configured), and ControlFLASH for firmware updates. It is equally suitable for connecting a laptop to a PanelView 550/600/700 terminal’s RS-232 configuration port (depending on terminal model and pinout—verify terminal manual) for terminal configuration or firmware service.Essential for first-time commissioning and disaster recovery: Even in Ethernet-capable systems, having a 1756-CP3​ on hand is considered best practice. When a new processor ships from the factory with no IP address, or when a corrupt EEPROM/image requires a direct serial download, or when the plant network is down for maintenance, the serial port + 1756-CP3​ is often the only way to regain access to the controller. Its inclusion in a field-service toolkit is a low-cost insurance measure against extended downtime.

Application Field

The Allen-Bradley 1756-CP3​ is principally used by automation engineers, system integrators, and maintenance technicians during the commissioning, programming, and troubleshooting phases of ControlLogix and SLC 500 based control systems. In a typical greenfield project, a ControlLogix 1756-L55 processor arrives from the factory with no application code and no IP address assigned. The engineer connects a laptop (via a USB-to-DB9 serial adapter + the 1756-CP3) to Channel 0 of the processor, configures a DF1 driver in RSLinx, goes online, sets the Ethernet module IP if present, downloads the application, and then may continue via Ethernet—but the initial bootstrap is almost always done through this serial cable.In brownfield retrofits or legacy plants where Ethernet infrastructure is absent or unreliable, the 1756-CP3​ serves as the primary day-to-day connection method for uploading programs for backup, making online edits to ladder logic, forcing bits for diagnostic purposes, and changing processor configuration words (S: files in SLC 500, GSV/SSV in ControlLogix). It is also indispensable for firmware upgrades using ControlFLASH, which historically required a stable serial link for older processor firmware versions before Ethernet firmware update was fully supported.Field service personnel carry the 1756-CP3​ (often with a known-good industrial USB-to-serial adapter) as part of a standard PLC service kit. When a machine goes down and the Ethernet cable has been cut, the switch is faulty, or the IP schema has been lost after a power outage, the technician can connect directly to the processor’s serial port with the 1756-CP3, go online, diagnose the fault, and—if necessary—perform an emergency download to restore operation. The right-angle connector is particularly appreciated in compact MCC buckets or machine-mounted enclosures where space behind the door is at a premium. For OEMs shipping SLC 500 or early ControlLogix machines, including a 1756-CP3​ in the spare-parts envelope ensures the end user has the correct cable to perform field service without calling the OEM for support.

Related Products

  • 1756-CP3 (Bulk / Spare)​ — The same 1756-CP3 cable; sometimes also referenced as the standard programming lead included with Rockwell starter kits (verify kit contents).
  • 1747-CP3​ — Older catalog number for essentially the same RS-232 null-modem DB9F-RA-to-DB9F cable; in practice the 1756-CP3 supersedes it and is used interchangeably for SLC 500 serial ports.
  • 1756-CFM​ — ControlLogix Counter/Frequency Module; unrelated functionally but often in the same chassis—note the 1756-CP3 does NOT connect to this module.
  • 1784-U2DHP​ — Allen-Bradley 1784-U2DHP USB-to-DH+ (Data Highway Plus) interface for SLC 500 / PLC-5 DH+ networks; used when DH+ (not RS-232 DF1) access is required—different protocol/cable than the 1756-CP3.
  • 1784-CP10​ — USB-to-Ethernet cable for certain MicroLogix 1100/1400 onboard Ethernet programming; not a substitute for the 1756-CP3 but an example of a modern direct-connect alternative where Ethernet is available.
  • 9355-WABOXENE​ — RSLinx Classicsoftware license (single-node); typically used in conjunction with the 1756-CP3 for driver configuration and going online via DF1.
  • 1747-BA / 1747-BAS / 1746-BAS​ — Legacy SLC 500 modules that are commonly accessed via the same 1756-CP3 / 1747-CP3 serial cable when performing uploads, downloads, or BASIC program editing.
  • Keyspan USA-19HS or equivalent industrial USB-to-DB9 Serial Adapter​ — Not a Rockwell product but commonly paired with the 1756-CP3​ on modern laptops lacking native DB9 COM ports; recommended to use a branded adapter with certified FTDI chipset for reliable DF1 communication.

 

Installation and Maintenance

Pre-installation preparation: Before using the 1756-CP3, confirm that the target processor (ControlLogix 1756-L55x or SLC 500 with DB9 RS-232 port) has its Channel 0 configured for DF1 Full-Duplex (System → Serial Port Settings in RSLogix 500 / 5000). If connecting through a USB-to-serial adapter on a laptop, install the adapter’s driver and note which COM port is assigned in Windows Device Manager. Connect the right-angle DB9 female end of the 1756-CP3​ to the processor’s RS-232 port (ensure it clicks/seats fully—the right-angle orientation should route the cable away from adjacent modules), and connect the straight DB9 female end to the PC’s COM port or USB-serial adapter. In RSLinx Classic, add a “DF1 Full-Duplex” driver, select the correct COM port, set the baud rate to match the processor’s Channel 0 setting (commonly 19200 or 38400 bps; default on many SLC/Logix is 19200), and apply—RSLinx should show the processor node appear in the RSWho window if the cable and port settings are correct.Maintenance recommendations: The 1756-CP3​ is a passive, non-powered interconnect cable with no user-serviceable elements. Inspect the molded DB9 connectors periodically for cracked housings, bent pins (especially on the straight-end that plugs into the PC/adapter—pins are male on the PLC side receptacle but the cable carries female shells), or frayed strain reliefs. If communication becomes intermittent, try a known-good USB-serial adapter first (many “comm failures” trace to the adapter, not the cable), then swap the 1756-CP3​ to rule out cable damage from repeated coiling or being pinched in cabinet doors. Store the cable loosely coiled (figure-8 style) in a dry compartment of the service kit; avoid tight kinking around the right-angle boot. There is no calibration or firmware associated with the 1756-CP3—if physical damage is evident and continuity fails on the TX/RX pins, replacement is the only remedy. Keeping at least one spare 1756-CP3​ in the maintenance crib is standard practice for plants with active SLC 500 or ControlLogix L55 installations.

Product Guarantee

We supply 100 % genuine Allen-Bradley 1756-CP3​ serial programming cables, each inspected for correct null-modem pinout continuity, shield integrity, and secure strain-relief molding prior to shipment. The 1756-CP3​ is covered by our standard warranty against defects in materials and workmanship under normal use. Our technical support team can assist with DF1 driver setup in RSLinx, baud-rate matching guidance, and compatibility confirmation with your specific ControlLogix or SLC 500 processor model and firmware revision. For legacy system support, we maintain availability of both current and discontinued Rockwell Automation accessories and can advise on suitable USB-serial adapters qualified for DF1 protocol communication. Your ability to reliably connect to, program, and troubleshoot your control system is our priority—every 1756-CP3​ we deliver is guaranteed to meet Rockwell Automation’s published specifications and perform dependably in field commissioning and maintenance applications.

Contact Us WhatsApp / Wechat：+86 18150087953
Phone：+86 18150087953
Email：sales@cxplcmro.com

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