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Configuring Modbus/BSAP
RLXIC-SV
♦
Intelligent Cellular
User Manual
RadioLinx Intelligent Cellular Serial Modem for the Verizon Wireless CDMA Network
ProSoft Technology, Inc.
Page 81 of 146
May 29, 2009
9 Configuring
Modbus/BSAP
In This Chapter
Modbus Overview.................................................................................. 81
Configuring the RLXIC-SV at the Polling Host for Modbus on UDP ...... 83
Configuring the Remote RLXIC-SVs for Modbus with UDP................... 85
The RLXIC-SV supports Modbus ASCII, Modbus RTU, BSAP, and can also
emulate other protocols like DF1 or others using its Modbus Variable feature.
9.1 Modbus
Overview
The Modbus Protocol, developed by Modicon in 1979, provides for client-server
(also referred to as master-slave) communications between intelligent devices.
As a de facto standard, it is the most widely used network protocol in the
industrial manufacturing environment to transfer discrete/analog I/O and register
data between control devices. Modbus, BSAP, and other Modbus variations are
often used in conjunction with telemetry devices.
Tip:
This section is just a brief overview of Modbus. For more information, refer to your Modbus
equipment distributor or manufacturer or http://www.modbus.org.
9.1.1 Telemetry
Telemetry is an automated communications process by which data is collected
from instruments located at remote or inaccessible points, and transmitted to
receiving equipment for measurement, monitoring, display, and recording. Trans-
mission of the information may be over physical pairs of wires,
telecommunication circuits, radios or satellite.
9.1.2 Remote Terminal Unit (RTU)
Modbus was originally designed to be used in a radio environment where
packets are broadcast from a central station (also called master or host) to a
group of remote units. Each remote unit, Remote Terminal Unit (RTU), has a
hexadecimal identification number (ID). The first part of the broadcast packet
contains an RTU ID which corresponds to the ID of one of the remote units. The
Modbus host looks for the ID, and sends to only the unit with the matching ID.
The RTU would then reply back to the central station.