User guide

Communication Capabiliites
890 USE 108 00 August 2001 91
Bridge Mode Between Modbus and Modbus Plus
Selecting
Standard or
Bridge
Communications
The standard Modbus port on the A984-145, E984-245/255/265/275/285
Controllers can be used in either of these two ways:
as a slave port to a Modbus master device
as a bridge between a Modbus master device and the Modbus Plus network
nodes
Make the above selection by setting the communication parameter slide switch as
follows:
setting the communication parameter slide switch (the bottom slide switch) on the
A984-145, E984-45/255 Controllers
setting the communication parameter slide switch (the bottom slide switch) on the
E984-265/275/285 Controllers
Settings for
Modbus Mode
For Modbus mode, set the switch to the mem position for the A984-145, E984-245/
255, and E984-/265/275/285 Controllers, and use the configuration editor to assign
the values for the Modbus port parameters.
Settings for
Bridge Mode
Bridge mode allows you to access nodes on a Modbus Plus network from a Modbus
master device (connected to the Modbus port).
Set Modbus Plus bridge mode, as follows:
For the E984-245/255 and A984-145 Controllers, set the slide switch to default
position, the controller’s bridge mode is automatically enabled.
For the E984-265/275/285 Controllers, set the slide switch to either ASCII or RTU
position, the controller’s bridge mode is automatically enabled. (See MODBUS
Port Parameters (3-Position Slide Switch), p. 76 for information about configuring
port parameters.)
Modbus Port
Parameter
Settings
The Modbus port parameters are set to 9600 baud, RTU mode (8 data bits and 1
stop bit), and even
parity, the same default conditions as the -120 and -130
Controllers.
Unique to the A984-145, E984-245/255, E984-265/275/285, however, is the default
port address. Instead of defaulting to Modbus port address 1, it defaults to the
Modbus Plus port address set by the DIP switch at the top of the (A984-145, E984-
245/255 PLCs) or by the rotary switches at the top of the (E984-265/275/285 PLCs).
Note: The Modbus Plus hardware address is always used in bridge mode.
If a software setting is used to enable bridge mode, all of the memory port
parameter settings are set by software except for the address parameter.