User guide

Communication Capabiliites
92
890 USE 108 00 August 2001
Modbus Master
Device
Connections
If a Modbus master device is connected to the Modbus port while the A984-145,
E984-245/255/265/275/285 is in bridge mode, the master device can be attached to
the local controller or to any other node on Modbus Plus.
If you attach to the local controller, messages from the Modbus master are sent
directly to the local A984-145, E984-245/255/265/275/285 without being routed
over a Modbus Plus communication path.
If you attach to any other node on the network, the message is routed through the
Modbus Plus port to the destination device.
If you are connecting a Modbus master device to a node on Modbus Plus, always
use the Modbus Plus address of the target node.
If you are attaching to the local Compact PLC in bridge mode, the master
automatically attaches to the Modbus Plus node address, which can only be set
by hardware -- either with the DIP switch (A984-145, E984-245/255) or with the
rotary switches (E984-265/275/285) on the local controller.
If you want to attach to any other Modbus Plus node, the Modbus master device
must specify that node by Modbus Plus address.
CAUTION
Failure to enter correct Modbus Plus address for controller.
If you are accustomed to using Modbus master devices (such as
programming panels) with Modicon programmable controllers in un-
networked environments, you may be used to attaching to the local
controller by addressing it as device #1-the default device address in
the configurator editor. Be aware that in a Modbus Plus network
environment you must know the Modbus Plus address of the controller
(or any other nodal device) with which you want to communicate, and
you must specify that address correctly in the attach procedure. If you
want to attach to a node on Modbus Plus but do not know its network
address, get this information from your network supervisor before
proceeding.
Failure to observe this precaution can result in injury or
equipment damage.
Note: When a Modbus port is used in bridge mode, it must be connected to a single
Modbus master device. That is, the bridge cannot be used as a connection for a
Modbus Slave device network.