Installation manual

Publication 1747-RM001G-EN-P - November 2008
SLC Communication Channels 13-5
DH-485 Network Initialization
Network initialization begins when a period of inactivity exceeds the time of a
link dead timeout. When the time for the link dead timeout is exceeded, usually
the initiator with the lowest address claims the token.
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. It will
wrap to node 0 upon reaching its maximum node address value.
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.
DH-485 Network Considerations
DH-485 Network 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 and higher - token hold factor
• Maximum number of communicating devices
• Broadcasting
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.