User Manual
Table Of Contents
- 1756-UM532A-EN-P
- Important User Information
- Table of Contents
- Purpose of This Manual
- Preface
- 1756-DH485 Module Overview
- Overview of the DH-485 Network
- Introduction
- DH-485 Network Description
- DH-485 Network Protocol
- DH-485 Token Rotation
- DH-485 Network Initialization
- Devices that Use the DH-485 Network
- 1747-AIC Isolated Link Coupler for DH-485
- 1761-NET-AIC Advanced Interface Converter Product Overview
- Operating Modes
- Device Compatibility
- Misconception about the 1761-NET-AIC Converter
- 1747-UIC USB to DH-485 Interface Converter
- Example System Configuration
- Important Planning Considerations
- Additional Resources
- Use Data Highway 485 Network
- Use RSLinx Software to Create a Routing Table
- Communicate from an SLC 5/03 Controller to a Logix Controller over a DH-485 Network
- Communicate Between SLC Controllers over DH+ and DH485 Networks
- Communicate Between a PLC-5 Controller and a Remote SLC 5/03 Controller over Multiple DH-485 Networks
- Communicate from an SLC 5/05 Controller to an SLC 5/03 Controller over an EtherNet/IP Network
- Communicate to a SLC 5/03 Controller on a DH-485 Network
- Communicate from a Logix Controller to an SLC 5/03 Controller over EtherNet/IP and DH-485 Networks
- Specifications
- Troubleshoot the 1756-DH485 Module
- Index
- How Are We Doing?
- Rockwell Automation Support
- Backcover

Publication 1756-UM532A-EN-P - May 2006
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Limitations of Remote DH-485 Messaging
Remote DH-485 messages are encapsulated in CIP messages and sent on CIP
connections when they are sent across ControlNet, EtherNet/IP, and the
ControlLogix chassis backplane. Although this is transparent to the user, there
are resource limits associated with CIP on the 1756-DH485 module.
The 1756-DH485 module supports up to 32 CIP connections. These
connections are made when devices want to send a DH-485 message out of a
1756-DH485 module’s DH-485 channel. The 1756-DH485 module makes
these connections when it receives DH-485 message traffic. The 1756-DH485
module recovers connections if they are not being used.
Because of the various paths involved, the 1756-DH485 module responds to
‘out of connections’ in one of the following ways:
• The 1756-DH485 module may generate a Routing Error on DH-485 for
DH-485 message requests if there are no connections available.
• The Message Originator may generate an application timeout if a remote
1756-DH485 module has no connections available for a DH-485
Message response.
For more information on application timeouts, refer to Application
Timeout on page 3-12.
• The Message Originator may receive an ‘out of connections’ error if the
path from the originator to the 1756-DH485 module is a ControlLogix
chassis, a ControlNet network, or an EtherNet/IP network.