Chapter 20: Modbus Communications; Modbus Overview; Modbus Slave Overview - HORNER APG EXL10 OCS User Manual

MAN1029-08-EN_EXL10_UserManual
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 EXL10 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 Modbus Addressing Section describes the supported Modbus Commands as well as the Modbus
Map for EXL10 References (%R, %M, etc.).
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