Online Ladder Logic Viewer
View PLC Diagrams Online
View Allen-Bradley ladder logic diagrams in your browser. No software installation required. Upload your L5X, ACD, or RSS file and instantly see color-coded rungs with AI-powered explanations.
What is Ladder Logic Programming?
Ladder logic is the most widely-used programming language for PLCs (Programmable Logic Controllers). It represents electrical circuits graphically, with two vertical power rails and horizontal rungs containing instructions. This visual format makes it intuitive for:
- Electricians familiar with relay schematics
- Maintenance technicians troubleshooting machines
- Controls engineers designing automation systems
- Operators understanding machine behavior
Each rung in a ladder diagram executes from left to right, evaluating conditions (inputs) before energizing outputs. This mimics how electrical current flows through relay logic circuits.
Understand Ladder Logic at a Glance
Our viewer uses intuitive color-coding to help you quickly identify different instruction types
Input Instructions
XIC, XIO contacts that examine bit states. Green indicates conditions being checked.
XIC, XIO, ONS, OSR, OSF
Output Instructions
OTE, OTL, OTU coils that control outputs. Red indicates actions being performed.
OTE, OTL, OTU
Timer Instructions
TON, TOF, RTO instructions for time-based control. Blue indicates timing operations.
TON, TOF, RTO, TONR
Counter Instructions
CTU, CTD, RES instructions for counting events. Purple indicates counting operations.
CTU, CTD, CTUD, RES
Math Instructions
ADD, SUB, MUL, DIV and other calculations. Amber indicates mathematical operations.
ADD, SUB, MUL, DIV, CPT
Compare Instructions
EQU, NEQ, GRT, LES for value comparisons. Cyan indicates comparison operations.
EQU, NEQ, GRT, LES, LIM
215+ Ladder Logic Instructions
From basic XIC/OTE to advanced motion control - every Allen-Bradley instruction rendered clearly
Bit Instructions
Timer/Counter
Compare
Math
Move/Logical
Array/File
Program Control
I/O & Communication
Motion Control
Get Plain English Explanations
Do not just view your ladder logic - understand it. Our AI analyzes each rung and explains what it does in plain English. Perfect for:
- Understanding unfamiliar code during troubleshooting
- Training new team members on existing programs
- Documenting machine behavior for operators
- Code reviews and knowledge transfer
- Cross-referencing tags across the entire project
- Identifying sensors, motors, valves, and safety devices automatically
- Detecting safety-critical logic and alarm conditions
- Comparing two program versions side by side
Friendly Mode
Simplified explanations for beginners. Uses everyday language without technical jargon.
Technical Mode
Detailed explanations for engineers. Includes timing, bit operations, and edge cases.
Operator Mode
Focused on machine behavior. Explains what the machine does, not how the code works.
View Any Allen-Bradley Format
Our ladder logic viewer supports all major Allen-Bradley file formats
View Your Ladder Logic Now
Upload your PLC file and start viewing ladder diagrams instantly
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Frequently Asked Questions
What is ladder logic?
Ladder logic is a graphical programming language used to program PLCs (Programmable Logic Controllers). It gets its name from its visual resemblance to a ladder, with two vertical rails (power rails) and horizontal rungs containing instructions. Each rung represents a logical operation, with inputs on the left (like switches and sensors) and outputs on the right (like motors and valves). Ladder logic was designed to mimic relay-based electrical schematics, making it intuitive for electricians and maintenance technicians to understand and troubleshoot.
How do I view ladder logic diagrams online?
With PLC Company, you can view ladder logic diagrams directly in your web browser without installing any software. Simply upload your L5X, ACD, or RSS file, and the viewer will parse and display all rungs with color-coded instructions. You'll see XIC contacts, OTE coils, timers, counters, and all other instructions rendered clearly. The viewer works on any device and files are encrypted in transit and processed on secure infrastructure.
What instructions does the viewer support?
PLC Company supports over 215 ladder logic instructions including: Bit instructions (XIC, XIO, OTE, OTL, OTU, ONS, OSR, OSF), Timer/Counter instructions (TON, TOF, RTO, CTU, CTD, RES), Compare instructions (EQU, NEQ, LES, GRT, LEQ, GEQ, LIM, MEQ), Math instructions (ADD, SUB, MUL, DIV, MOD, SQR, NEG, ABS), Move instructions (MOV, MVM, BTD, SWPB, CLR), Array instructions (COP, CPS, FLL, AVE, SRT, STD), Program control (JSR, RET, JMP, LBL, MCR, AFI), and many more including motion control, message, and diagnostic instructions.
Can I get explanations of ladder logic rungs?
Yes! PLC Company includes AI-powered explanations that describe what each rung does in plain English. Click on any rung and choose from three explanation modes: Friendly (simplified explanations for beginners), Technical (detailed explanations for engineers), or Operator (focused on what the machine does). The AI considers tag names, comments, and instruction context to provide meaningful, accurate explanations of your ladder logic.