Rockwell Automation 1756-DH485 ControlLogix DH-485 Communication Module User Manual - Manual (Page 31)

Publication 1756-UM532A-EN-P - May 2006
Overview of the DH-485 Network 2-13
Maximum Node Address Setting
The maximum node address parameter should be set as low as possible. This
minimizes the amount of time used in soliciting successors when initializing
the network. If all nodes are addressed in sequence from 0, and the maximum
node address is equal to the address of the highest addressed node, the token
rotation will improve by the amount of time required to transmit a solicit
successor packet plus the slot timeout value.
You cannot add any nodes to the network without affecting the response time.
On the other hand, since the time required to hold an open station address is
greater than the time required to pass a token, it can be useful to leave a
temporary device (such as a personal computer) connected if there is only one
such device. A solicit successor packet requires the same transmission time as
the token pass, but there is an added slot timeout period.
See your programming software user manual for the procedures to set node
addresses, controller baud rate, and maximum node addresses.
Maximum Number of Communicating Devices
SLC 500 fixed and SLC 5/01 controllers can be selected by two initiators
maximum at the same time. Using more than two initiators to select the same
SLC 500 fixed and SLC 5/01 controllers at the same time can cause
communication timeouts.
Additional Resources Refer to the manuals listed in the table Devices that Use the DH-485 Network
on page 2-3.
IMPORTANT
The SLC 500 Series A (only) controllers set the maximum
node address to 31 when power is cycled increasing
initialization and response time of the network.