Sierra Wireless AirLink RV50 Series User Manual page 350

ALEOS 4.9.0 Software Configuration User Guide for AirLink RV50 Series
Rev 1 Dec. 17
Programmable Logic Controller (PLC)
A Programmable Logic Controller (PLC) is a small industrial computer which
generally monitors several connected sensor inputs and controls attached
devices (motor starters, solenoids, pilot lights/displays, speed drives, valves, etc.)
according to a user-created program stored in its memory. Containing inputs and
outputs similar to an RTU, PLCs are frequently used for typical relay control,
sophisticated motion control, process control, Distributed Control System and
complex networking.
Modbus TCP/IP
Modbus TCP/IP simply takes the Modbus instruction set and wraps TCP/IP
around it. Since TCP/IP is the communications standard for the Internet and most
networked computers, this provides a simpler installation. Modbus TCP/IP uses
standard Ethernet equipment.
Modbus on UDP
When Sierra Wireless AirLink gateways are used in place of radios, a AirLink
gateway is connected to the central station (host) and an AirLink gateway is
connected to each remote unit. When the AirLink gateway is configured for
Modbus with UDP, the AirLink gateway connected to the host can store a list of IP
addresses or names with matching IDs. When the host at the central station
sends serial data as a poll request, the AirLink gateway at the host matches the
RTU ID to a corresponding IP of a AirLink gateway at a remote unit. A UDP
packet is assembled encapsulating the RTU ID and serial data transmitted from
the host. The UDP packet is then transmitted to the specific AirLink gateway at
the remote unit matching the RTU ID. The remote AirLink gateway then
disassembles the packet before transmitting the RTU ID and serial data to the
remote unit. The remote units operate in normal UDP mode and their data is sent
to the host via the remote AirLink gateway and host AirLink gateway.
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