User guide

Communication Capabiliites
890 USE 108 00 August 2001 79
Generic Modbus Communication Functions
Modbus
Communication
Modes
Modbus can operate in two communication modes: ASCII (the ANSI standard for
inter-device communications) and RTU.
How to Specify
Modbus Port
Parameters
For the A984 and E984-241/251, refer to MODBUS Port Parameters (2-Position
Slide Switch), p. 71. For the E984-258/265/275/285, refer to MODBUS Port
Parameters (3-Position Slide Switch), p. 76. Use of this switch in the context of
Modbus Plus communications is discussed in Communication Parameters Slide
Switch -Bridge Mode, p. 83.
Setting Up a
Communications
Network Over
Modbus
Modbus also provides a cost-effective method for handling remote programming
and data transfer over a master-slave nodal network. Modbus allows you to link
Compact Controllers and other Modicon Programmable Controllers with computer
terminals or programming panels for data acquisition, supervisory control, and
programming functions.
Up to 247 slave nodes can be linked on a Modbus network, and communications
can occur at data rates of up to 19,200 baud over twisted pair cable, common carrier
phone lines, or microwave transmitters.