Modbus/Bsap Configuration; Modbus Overview - Sierra Wireless AirLink RV50 Series User Manual

B: Modbus/BSAP Configuration
The AirLink gateway supports Modbus ASCII, Modbus RTU, and BSAP, and can also
emulate other protocols (like DF1) using the Modbus Variable feature.

Modbus Overview

The Modbus Protocol provides for client-server (i.e., 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 www.modbus.org.
Telemetry
Telemetry is an mated 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. Transmission of the
information may be over physical pairs of wires, telecommunication circuits, radios, or
satellites.
Remote Terminal Unit (RTU)
Modbus was originally designed to be used in a radio environment where packets
were broadcast from a central station (i.e., master or host) to a group of remote units.
Each remote unit, or 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 only sends to the unit with the matching ID; the RTU then replies back to the
central station.
The RTU connects to such physical equipment as switches, pumps, and other
devices, and monitors and controls these devices. The RTU can be part of a network
set up for Supervisory Control and Data Acquisition.
Supervisory Control and Data Acquisition (SCADA)
Supervisory Control and Data Acquisition (SCADA) describes solutions across a
large variety of industries and is used in industrial and engineering applications to
monitor and control distributed systems from a master location. SCADA
encompasses multiple RTUs, a central control room with a host computer (or
network), and some sort of communication infrastructure.
SCADA allows for "supervisory" control of remote devices as well as acquiring data
from the remote locations. Programmable Logic Controllers allow for a higher degree
of mated SCADA.
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