Introduction – Reliable DH-485 Connectivity for ControlLogix Systems

The Allen Bradley 1756-DH485 is a ControlLogix DH-485 Communication Module developed for applications that require communication between ControlLogix controllers and established DH-485 networks. It provides two independent DH-485 channels, making it particularly useful when integrating legacy Allen Bradley equipment into an existing automation architecture.

With two 9-pin D-shell communication ports, the module supports data exchange across separate DH-485 network connections. This capability helps industrial facilities maintain communication between different generations of control equipment without requiring an immediate replacement of the entire automation infrastructure.

The 1756-DH485 is suitable for maintenance projects, legacy PLC integration, and industrial system upgrades where continuity and compatibility are important considerations. Its installation within a ControlLogix chassis also allows it to become part of an established modular control platform.

For maintenance teams and industrial equipment purchasers, the 1756-DH485 remains a relevant replacement option for existing DH-485 installations. When selecting this module, verify the catalog number, series, network requirements, and chassis compatibility to ensure the replacement meets the original system configuration.

Technical Specifications – Product Data & Electrical Characteristics

The following table summarizes the main hardware, communication, and electrical specifications of the Allen Bradley 1756-DH485.

Parameter	Specification
Brand	Allen Bradley
Model	1756-DH485
Product Type	ControlLogix Communication Module
Communication Protocol	DH-485
Communication Channels	2 Independent Channels
Communication Ports	2 × 9-pin D-shell
Communication Rate	9,600 bps / 19.2 kbps
Backplane Current (5.1V DC)	850 mA
Backplane Current (24V DC)	1.7 mA
Maximum Power Dissipation	4.5 W
Thermal Dissipation	15.4 BTU/hr
Isolation Voltage	50V Continuous
Slot Width	1 Slot
Installation Location	ControlLogix Chassis
Operating Temperature	0–60°C
Storage Temperature	-40–85°C
Relative Humidity	5–95%, Non-condensing
Dimensions	144.5 × 34.6 × 130.18 mm
Weight	0.272 kg / 0.60 lb

Physical Dimensions and Weight

Length: 144.5 mm
Width: 34.6 mm
Height: 130.18 mm
Net Weight: 0.272 kg (0.60 lb)

These specifications are useful when evaluating replacement requirements, chassis installation, and compatibility with existing ControlLogix equipment.

Recommended Related Models – Compatible Communication Accessories

The following Allen Bradley products are relevant to DH-485 integration, legacy network connectivity, and ControlLogix communication applications.

Model	Product Description
1761-NET-AIC	Advanced Interface Converter
1747-CP3	RS-232 Communication Cable
1761-CBL-AC00	Communication Cable
1761-CBL-AP00	Communication Cable
1761-CBL-PM02	Communication Cable
1756-DHRIO	ControlLogix Data Highway Plus / Remote I/O Communication Module

These products can be considered when planning DH-485 network connections, maintaining legacy equipment, or servicing an established ControlLogix installation. Always verify the required cable and interface configuration before ordering.

Popular Related Models – Allen Bradley ControlLogix Communication Series

For customers maintaining or expanding ControlLogix automation systems, the following communication modules are also worth considering.

Model	Product Description
1756-ENBT	ControlLogix EtherNet/IP Communication Module
1756-EN2T	ControlLogix EtherNet/IP Communication Module
1756-EN2TR	ControlLogix EtherNet/IP Communication Module
1756-CN2R	ControlLogix ControlNet Communication Module
1756-DHRIO	ControlLogix DH+/Remote I/O Communication Module
1756-CNB	ControlLogix ControlNet Bridge Module
1756-EN2F	ControlLogix EtherNet/IP Fiber Module

Whether you are replacing an existing communication module or sourcing components for an industrial automation maintenance project, selecting the correct Allen Bradley catalog number is essential. We support industrial automation equipment sourcing and can help customers identify suitable ControlLogix components for their existing systems.

Applications

The Allen Bradley 1756-DH485 ControlLogix Communication Module is intended for industrial communication environments where reliable data exchange between control devices and legacy automation equipment is important. Within a ControlLogix-based architecture, communication interfaces help connect controllers with field-level devices and supporting control systems.

Typical application areas include:

Industrial Automation Networks: Supporting communication between automation equipment and control systems.
Legacy System Integration: Helping maintain connectivity in installations that incorporate older Allen Bradley control equipment.
Manufacturing Operations: Supporting data exchange in production lines, assembly systems, and automated machinery.
Process Control: Forming part of communication architectures used in industrial process monitoring and control.
System Modernization: Supporting maintenance and integration projects involving existing control infrastructure.

Advantages

Integration Flexibility

Communication modules are an important part of a distributed automation architecture. They help establish connections between control equipment and other devices, making system integration and maintenance more manageable.

Designed for Industrial Environments

The ControlLogix platform is built for demanding industrial applications. Its modular architecture allows users to configure control systems around specific operational requirements.

Simplified System Expansion

A modular communication architecture provides flexibility when developing or upgrading an automation installation. It can help reduce the need for extensive changes to the overall control structure.

Long-Term Maintenance Support

For facilities operating established automation systems, maintaining compatibility with existing equipment is often more practical than replacing an entire control network. Selecting the correct communication hardware can support a more controlled modernization process.

Practical Replacement Considerations

When sourcing a replacement module, matching the exact catalog number, hardware revision, firmware compatibility, and network requirements is essential to maintaining stable operation.

Technical FAQs – Configuration, Networking & Maintenance

Q1. What communication protocol does the 1756-DH485 support?

The 1756-DH485 supports the Data Highway 485 (DH-485) protocol. It allows ControlLogix systems to exchange messages with devices operating on an existing DH-485 network.

Q2. How many DH-485 communication channels are available?

The module provides two independent DH-485 communication channels, allowing connections to two separate DH-485 network segments.

Q3. What physical connectors are provided on the module?

The 1756-DH485 is equipped with two 9-pin D-shell connectors, one for each DH-485 communication channel.

Q4. What communication speeds does the 1756-DH485 support?

The supported communication rates are 9,600 bps and 19.2 kbps. The selected rate must be consistent with the connected network devices.

Q5. Can the 1756-DH485 communicate with Allen Bradley SLC 500 controllers?

Yes. The module is designed to bridge DH-485 messages between a ControlLogix chassis and compatible devices on a DH-485 network, including SLC 500 controllers.

Q6. Does the module require a ControlLogix chassis?

Yes. The 1756-DH485 is installed directly into a compatible ControlLogix chassis and receives its operating power through the chassis backplane.

Q7. Is an additional interface converter required for DH-485 network connections?

A 1761-NET-AIC Advanced Interface Converter is used where required by the network connection arrangement. Appropriate communication cables must also be selected for the connected equipment.

Q8. Can the 1756-DH485 support remote programming and monitoring?

Yes. DH-485 connectivity supports remote programming and monitoring through compatible Rockwell Automation programming environments. Actual functionality depends on the connected controller, network configuration, and software version.

Q9. What should be checked if a DH-485 channel fails to communicate?

Inspect the communication cable, connector condition, network wiring, node configuration, and communication speed. Check the channel status indicators to determine whether the channel is offline or reporting a hardware fault.

Q10. Can the 1756-DH485 be used in a new ControlLogix network installation?

It can be used when integration with an existing DH-485 network is required. For new ControlLogix installations, modern open-network communication solutions are generally preferable, depending on system architecture and application requirements.

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