Controls › PLC Systems
Communications
The protocols that move data between controllers, devices, and SCADA.
Written guides in this section
Full references, procedures, and diagnostic guides published under Communications.
EtherNet/IP
How EtherNet/IP moves control data: CIP over standard Ethernet, implicit I/O connections on a requested packet interval, explicit messaging, producer and consumer tags, and what the network has to provide.
9 min readUpdated Sep 5, 2026
DNP3
The protocol built for utility telemetry: master and outstation, static and event data classes, unsolicited reporting, time-stamped events, and why it suits slow links that Modbus does not.
8 min readUpdated Sep 5, 2026
OPC UA
What OPC UA is for, how its information model, security, and transports differ from OPC Classic, where it belongs in a plant, and what to check before relying on it.
8 min readUpdated Sep 5, 2026
Serial Communications
RS-232, RS-422, and RS-485 in practice: which is which, cable and distance, termination, biasing, the common reference wire everyone leaves off, and the settings that have to match at both ends.
9 min readUpdated Sep 5, 2026
Protocol Gateways
Protocol converters between a controller and devices that do not speak its language: what a gateway does, the common pairings in water and wastewater, the mapping table that is the whole configuration, the failure modes a gateway adds, and when to use a native interface instead.
9 min readUpdated Sep 5, 2026
Remote I/O
Extending controller I/O to another panel or another site over a network: the adapter and the rack, the update rate and what it costs, what the outputs do when the link fails, the difference between remote I/O and a remote controller, and the wiring, addressing, and diagnostics that make it dependable.
9 min readUpdated Sep 5, 2026
Topics in this area
Modbus RTU
Serial Modbus: registers, function codes, addressing, and the framing rules that trip people up.
Modbus TCP
Modbus over Ethernet, unit IDs, and what changes when you leave RS-485 behind.
EtherNet/IP
CIP over Ethernet: implicit I/O, explicit messaging, and RPI.
DNP3
The utility protocol built for unsolicited reporting and time-stamped events.
OPC UA
A modern, secure, platform-independent data exchange standard.
Serial Communications
RS-232, RS-422, RS-485, biasing, termination, and cable practice.
Gateways
Protocol converters, when they help, and the failure modes they add.
Remote I/O
Extending I/O to a remote panel or a remote site.
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