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FUNCTION_BLOCK FB1
VAR_INPUT
Start : BOOL;
Speed : INT;
END_VAR
VAR_OUTPUT
Running : BOOL;
Error : BOOL;
END_VAR
BEGIN
IF Start AND NOT Error THEN
Running := TRUE;
IF Speed > 1500 THEN
Error := TRUE;
Running := FALSE;
END_IF;
ELSE
Running := FALSE;
END_IF;
END_FUNCTION_BLOCKMotor Control Block (FB1) This function block implements a basic motor control with overspeed protection. Inputs: • Start (BOOL) – Motor start command • Speed (INT) – Current motor speed in RPM Outputs: • Running (BOOL) – Motor active flag • Error (BOOL) – Fault indicator Safety Logic: ⚠️ Overspeed protection triggers at 1500 RPM. Motor stops and error flag is set. Recommendation: Add hysteresis to prevent rapid on/off cycling near the speed threshold.
How it works
Three simple steps to understand any PLC program.
Paste your code
Copy a block from STEP 5, STEP 7 or TIA Portal. Or upload an .awl file.
Understand instantly
The AI explains your code network by network. Free, no sign-up required.
Get more done
Need documentation for your boss? Code migration? From €49/month.
What PLCcheck can do
Explain is free and unlimited. Everything else from €49/month.
Understand unfamiliar code in seconds
Summary, network-by-network explanation, detected patterns and safety warnings. Free, unlimited.
Generate complete documentation with I/O table
Professional documentation with I/O tables, timer lists and block descriptions. Ready for audits.
Convert S5→S7-SCL automatically
Translate AWL/STL code to clean SCL. Instruction mapping, address conversion and symbol generation.
Find dead code and improvements
Detect unused variables, inefficient logic and missing error handling.
Free PLC Tools
View All Tools →S5 Timer Calculator
Convert KT timer values to seconds, IEC format, and S7 code.
Open →S5→S7 Address Converter
Convert S5 addresses to S7 equivalents with ×2 rule for data blocks.
Open →AWL Command Lookup
Search all 40 S5 AWL commands with S7 equivalents and SCL.
Open →S5→S7 Command Converter
Paste S5 AWL code, get S7 STL + SCL instantly.
Open →PLC Code Validator
Paste AWL or SCL code and get instant syntax and logic checks.
Open →Migration Estimator
Estimate migration effort, cost, and timeline for your plant.
Open →Popular Migration Guides
Browse All Guides →S5 to S7 Migration: The Complete Guide
Step-by-step guide for migrating Siemens S5 PLC programs to S7-1500.
Read Guide →S7-300 End-of-Life: Migration Planning Guide
What the S7-300 phase-out means for your plant and how to plan the migration.
Read Guide →PLC-5 to ControlLogix Migration Guide
Complete guide for migrating Allen-Bradley PLC-5 to ControlLogix.
Read Guide →PLC Reference Library
Browse Full Reference →S5 AWL Command Reference
Complete reference of all 40 S5 AWL instructions with S7 equivalents, syntax, and examples.
S7 SCL Reference
SCL syntax, timers, counters, math operators, data types, and best practices.
S5→S7 Address Mapping
I/O, markers, data blocks, periphery, and counter format conversion tables.
Timer Conversion
S5 KT timer format to IEC timers (TON/TOF/TP). Time base reference and BCD encoding.
IEC 61131-3
Programming languages, data types, and standard function blocks.
Simple, transparent pricing
Start free. Upgrade when you're ready.
Free
Understand code — instantly and unlimited.
- Explain — unlimited
- Network-by-network analysis
- Pattern detection & safety warnings
- No sign-up required
Starter
For active automation engineers.
- Explain — unlimited
- Document & Migrate
- 30 analyses/month (Doc+Migrate)
- PDF export & SCL download
- Save analysis history
Pro
For professional automation engineers.
- Explain — unlimited
- Document & Migrate — unlimited
- Optimize
- Everything in Starter
- API access
- Up to 5 plants
Team
For engineering teams and integrators.
- Everything in Pro
- 5 team members included
- Shared workspace
- Unlimited plants
- Admin dashboard
- SSO integration
Real problems PLCcheck solves
These are actual challenges from PLC engineering forums — not marketing claims.
“I've been given the honorable task of migrating a plant from S5 to S7. I've never worked with S5 before.”
SPS-Forum.de — Typical request
PLCcheck explains the S5 code line by line and generates the S7 migration automatically.
“Nobody knows how the plant actually works. There's a printout from 1995, no one knows if it's up to date.”
SPS-Forum.de — Typical request
PLCcheck documents the code and creates an up-to-date I/O table in seconds.
“The converted program looks terrible. Edge flags are done in a roundabout way, symbolic addressing is missing.”
SPS-Forum.de — About the Siemens converter
PLCcheck migrates to clean SCL with symbolic variables and IEC timers.
Frequently asked questions
- What PLC languages are supported?
- Siemens S5-AWL, S7-STL/AWL, and SCL (TIA Portal Structured Text). The code format is detected automatically. Just paste your code.
- Is my code secure?
- Yes. Your code is transmitted encrypted, not stored, and never used for AI training. Our servers are located in Frankfurt (EU). For companies with strict data protection requirements, we are planning an on-premise version.
- How accurate is the AI analysis?
- PLCcheck uses specialized analysis prompts that recognize S5/S7 patterns like self-holding circuits, sequence chains, timer formats and safety logic. We always recommend manual review for safety-critical applications.
- Can I use PLCcheck offline?
- PLCcheck is currently a cloud-based tool. An on-premise version for enterprise customers with strict data policies is planned. Contact our sales team for early access.
- What does PLCcheck cost?
- Explaining your code is completely free and unlimited — you don't even need an account. For documentation and migration there's the Starter plan from €49/month.
- What is the difference between Explain and Document?
- Explain gives you a readable analysis of your code — what each network does, which patterns are present, where the risks are. Document generates formal technical documentation with I/O table, timer list and cross-references — ready to print for audits or project handovers.