IMO i3C Lite, User Manual

Page: 158 / 167

Page | 158
CHAPTER 19: MODBUS COMMUNICATIONS
19.1 Modbus Overview
For complete Modbus instructions, please refer to the Help file in I³ Config .
Modbus (serial) is a popular, de-facto standard protocol that allows industrial devices from multiple
manufacturers to easily share data in real-time. For Modbus serial communications, the
i ³C Lite. can
act as either a Master or a Slave.
Modbus protocol (serial) allows for one master and multiple slaves. The master always initiates the
conversation by sending a request to a particular slave. Only the addressed slave will send a
response when the request is completed. Should the slave be unable to complete the request, it
returns the appropriate error response. Should the slave
be unable to respond, the master’s timeout
timer expires to provide an indication of No Response .
19.2 Modbus Slave Overview
For complete Modbus Slave instructions , please refer to the Help file in i ³ Config .
The Modbus slave function block, when used with the appropriate Modem and/or Open function
blocks, allows the primary serial port on the controller to act as a Modbus slave. The Modbus
function supports both ASCII and RTU modes of operation across a range of baud rates and protocol
frames. Also supported is port activity status, an inactivity timer, support for call-on exception, and
support for store and forward (repeater) operation for radio modems.
Section 19.5 describes the supported Modbus Commands as well as the Modbus Map for
i ³C Lite.
References (%R, %M, etc.).