PLC — Programmable Logic Controller Reference

Quick-reference skill for PLC programming concepts, IEC 61131-3 languages, common instruction sets, and troubleshooting patterns.

When to Use

• Writing or reviewing ladder logic programs
• Debugging PLC faults and I/O issues
• Choosing between Structured Text, Function Block, or Ladder
• Looking up IEC 61131-3 data types and timer/counter instructions
• Setting up communication protocols (Modbus, EtherNet/IP, Profinet)

Commands

intro

scripts/script.sh intro

Overview of PLC architecture — CPU, I/O modules, scan cycle, memory areas.

languages

scripts/script.sh languages

IEC 61131-3 programming languages: Ladder Diagram (LD), Structured Text (ST), Function Block Diagram (FBD), Instruction List (IL), Sequential Function Chart (SFC).

instructions

scripts/script.sh instructions

Common PLC instructions — contacts, coils, timers (TON/TOF/TP), counters (CTU/CTD), math, comparison, move.

datatypes

scripts/script.sh datatypes

IEC 61131-3 data types: BOOL, INT, DINT, REAL, STRING, TIME, arrays, structs.

faults

scripts/script.sh faults

Common PLC fault codes and troubleshooting steps — CPU faults, I/O faults, communication errors.

protocols

scripts/script.sh protocols

Industrial communication protocols — Modbus RTU/TCP, EtherNet/IP, Profinet, DeviceNet, OPC UA.

examples

scripts/script.sh examples

Example programs: motor start/stop, traffic light sequence, tank level control, conveyor interlock.

checklist

scripts/script.sh checklist

Pre-commissioning checklist — wiring, grounding, I/O mapping, safety circuit verification.

help

scripts/script.sh help

version

scripts/script.sh version

Configuration

Variable	Description
PLC_DIR	Data directory (default: ~/.plc/)

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