Installation manual

Publication 1747-RM001G-EN-P - November 2008
13-6 SLC Communication Channels
Setting Node Addresses
The best network performance occurs when node addresses start at 0 and are
assigned in sequential order. SLC 500 processors default to node address 1.
The node address is stored in the processor status file (S:15L). Processors
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.
If some nodes are connected on a temporary basis, do not assign addresses to
them. Simply create nodes as needed and delete them when they are no longer
required.
Setting Processor Baud Rate
The best network performance occurs at the highest baud rate. All devices
must be at the same baud rate. The default DH-485 baud rate for SLC 500
devices is 19.2K baud. The baud rate is stored in the processor status file
(S:15H).
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.
Maximum Number of Communicating Devices
SLC 500 fixed and SLC 5/01 processors can be selected by no more than two
initiators at the same time. Using more than two initiators to select the same
SLC 500 fixed and SLC 5/01 processors at the same time can cause
communication time-outs.
Broadcasting
A broadcast write command is sent as a DH-485 Send Data No
Acknowledgement (SDN) packet. No acknowledgement or reply is returned.
Broadcasting is the most efficient way to write the same data to multiple
devices on the DH-485 network.