Description
The Allen-Bradley 1756-DH485 is a specialized communication interface bridge module designed for the ControlLogix automation platform. This single-slot module functions as a protocol gateway, enabling ControlLogix processors to interface directly with legacy DH-485 (Data Highway 485) networks. It is an essential component for system migrations, allowing for the integration of legacy SLC 500, MicroLogix, or PanelView hardware into high-performance ControlLogix systems without requiring complete field rewiring.
Features
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Dual-Channel Connectivity: Features two independent DB9 communication ports (Channel A and Channel B), allowing for flexible network configuration as either an initiator or a responding node.
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Network Capacity: Supports up to 32 logical devices per network segment.
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Galvanic Isolation: Integrated electrical isolation barriers protect internal backplane logic from ground-loop fluctuations and field surges.
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Protocol Support: Utilizes standard token-passing protocol layers over RS-485 physical media.
Applications
This module is primarily used in industrial environments for phased equipment retrofits and system upgrades. It allows facilities to maintain communication with legacy DH-485 devices while transitioning to modern ControlLogix control architectures, effectively reducing implementation costs and minimizing system downtime.
Technical Specifications
| Model |
1756-DH485 |
| Product Line |
ControlLogix |
| Module Type |
DH-485 Communication Bridge |
| Ports |
2x DB9 D-shell (Channel A/B) |
| Baud Rates |
9.6 kbps, 19.2 kbps |
| Backplane Current (5.1V) |
850 mA |
| Backplane Current (24V) |
1.7 mA |
| Power Dissipation |
4.5 Watts |
| Isolation Voltage |
30V continuous |
| Operating Temperature |
0 to 60 deg C |
| Humidity |
5 to 95 percent non-condensing |
Installation Guidelines
- Ensure the ControlLogix chassis is powered down before inserting or removing the module.
- The module occupies a single slot in any standard 1756 ControlLogix chassis.
- Use shielded communication cables for RS-485 connections to minimize EMI interference.
- Ensure proper grounding of the chassis to a common earth ground to maintain signal integrity.
- Handle the module using ESD-safe practices to prevent damage to sensitive electronic components.
FAQ
Can this module be used in any ControlLogix chassis?
Yes, the 1756-DH485 is compatible with standard 1756 chassis series, including 1756-A4, 1756-A7, 1756-A10, 1756-A13, and 1756-A17.
Does the module require external power?
No, the module is powered directly through the ControlLogix backplane; it does not require an external power supply for its own operation.
