Rockwell Automation 1756-DH485 ControlLogix DH-485 Communication Module User Manual - Manual (Page 30)

Publication 1756-UM532A-EN-P - May 2006
2-12 Overview of the DH-485 Network
Software Considerations
Software considerations include the configuration of the network and the
parameters that can be set to the specific requirements of the network. The
following are major configuration factors that have a significant effect on
network performance:
• Number of nodes on the network
• Addresses of those nodes
• Baud rate
• Maximum node address selection
• SLC 5/03, SLC 5/04, and SLC 5/05 controllers only: token hold factor
• Maximum number of communicating devices
The following sections explain network considerations and describe ways to
select parameters for optimum network performance (speed).
Number of Nodes
The number of nodes on the network directly affects the data transfer time
between nodes. Unnecessary nodes (such as a second programming terminal
that is not being used) slow the data transfer rate. The maximum number of
nodes on the network is 32.
Set Node Addresses
The best network performance occurs when node addresses start at 0 and are
assigned in sequential order. Controllers cannot be node 0. Also, initiators such
as personal computers should be assigned the lowest numbered addresses to
minimize the time required to initialize the network.
Set Controller Baud Rate
The best network performance occurs at the highest baud rate. All devices
must be at the same baud rate.