MAN1106-07-EN_XL+_UserManual
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CHAPTER 20: MODBUS COMMUNICATIONS
20.1 Modbus Overview
For complete Modbus instructions, please refer to the Help file in Cscape.
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 XL+ 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.
20.2 Modbus Slave Overview
For complete Modbus Slave instructions, please refer to the Help file in Cscape.
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.
The
section describes the supported Modbus Commands as well as the
Modbus Map for XL+ References (%R, %M, etc.).
