Rockwell Automation 5730 DriveLogix5730 Controller for PowerFlex 700S Drives with Phase II Control - Manual (Page 183)

Communicating with Devices on a DH485 Link 9-5
The allowable range of the node address of an initiator is 0 to 31. The
allowable address range for all responders is 1 to 31. There must be at least
one initiator on the network.
Network Initialization
The network requires at least one initiator to initialize it. Network
initialization begins when an initiator on the network detects a period of
inactivity that exceeds the time of a link dead timeout. When the link dead
timeout is exceeded, usually the initiator with the lowest address claims the
token. When an initiator has the token it will begin to build the network.
Building a network begins when the initiator that claimed the token tries to
pass the token to the successor node. If the attempt to pass the token fails, or
if the initiator has no established successor (for example, when it powers
up), it begins a linear search for a successor starting with the node above it
in the addressing.
When the initiator finds another active initiator, it passes the token to that
node, which repeats the process until the token is passed all the way around
the network to the first node. At this point, the network is in a state of
normal operation.
Number of Nodes and Node Addresses
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.
If the node addresses for controllers are assigned in sequence, starting at
node 1 (with node 0 left for a programming terminal), it is as efficient to
leave the maximum node address at 31 as it is to decrease it to the highest
node address on the network. Then, adding devices to the network at a later
time will not require modifying the maximum node address in every device
on the network. The maximum node address should be the same for all
devices on a DH-485 network for optimal operation.
The best network performance occurs when node addresses start at 0 and
are assigned in sequential order. The controller defaults to node address 1
(controllers cannot be node 0). Initiators, such as personal computers,
should be assigned the lowest numbered addresses to minimize the time
required to initialize the network.