Rockwell Automation 1756-DHRIO_DHRIOXT ControlLogix Data Highway Plus-Remote I/O Communication Interface Module - Manual (Page 22)

22 Rockwell Automation Publication 1756-UM514C-EN-P - June 2014
Chapter 2 Using the Data Highway Plus Network
Link Design
When you design your DH+ link, use good design practices, including laying out
the link before installation. We also recommend you consider the following when
designing your DH+ link:
• All performance requirements
• Maintenance
• Possible future changes to the link
Use a1770-CD (Belden 9463) cable to connect your 1756-DHRIO module to
DH+. Use a Belden 89463 cable to connect your 1756-DHRIOXT module to
DH+. Connect a DH+ network by using a daisy chain or trunk line/drop line
configuration.
Trunk Line/Drop Line Considerations
When using a trunk line/drop line configuration, use 1770-SC station
connectors and follow these cable-length guidelines:
• trunk line-cable length - depends on the communication rate of the link
• drop-cable length - 30.4 m (100 cable-ft.)
Verify that your system’s design plans specify cable lengths within allowable
measurements.
For daisy chain configurations, use the following table to determine the available
total cable length.
For proper operation, terminate the ends of a DH+ link by using the external
resistors shipped with the module. The following table lists the resistors you can
use with each communication rate.
IMPORTANT The maximum cable length for DH+ depends on the transmission rate.
Configure all devices on a DH+ link to communicate at the same
transmission rate.
A DH+ link using this communication rate: Cannot exceed this cable length:
57.6 kbps 3,048m (10,000 ft)
115.2 kbps 1524m (5,000ft)
230.4 kbps 762m (2,500 ft)
If your DH+ I/O link operates at: Use this resistor rating:
57.6 kbps 150
Ω
115.2 kbps 150
Ω
230 kbps 82
Ω