bytesagain 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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