What you will be able to do
- Read and write the core Logix, S7, GX Works and IEC instructions in each vendor's own terms
- Say what a contact, coil, timer, counter, compare or one-shot does on each platform, and where the names differ
- Use each vendor's addressing: tags, absolute areas, device letters and direct addresses
- Explain how the scan or cycle differs between the platforms and where scan time is reported
- Translate a motor start/stop between the four dialects
Read a BOOL tag as a normally open contact and combine two of them in series to build a permit.
Use the normally closed contact so a fault bit blocks a rung, and see why the fault logic reads the opposite way to the wiring.
Learn why an OTE drops with its rung, and fix the duplicate-OTE bug where the last rung scanned silently wins.
Hold an alarm bit on after the trigger has gone and clear it only with a deliberate unlatch rung.
Start a pump three seconds after a request and read the timer's done bit instead of the request itself.
Run a cooling fan on for a fixed time after the motor stops, using the off-delay timer's done bit.
Count five parts into a box with a count-up counter and clear it with a separate reset.
Toggle a light once per push-button press by turning the button level into a single-scan pulse.
Turn a tank level into high and low lamps with strict greater-than and less-than limits.
Combine a normally open selector with a normally closed interlock, and read the same logic in STL.
Merge two alarm conditions into one assignment instead of writing the same output twice.
Latch a motor with S and R and decide who wins when both conditions are true, using statement order.
Delay a pump start with an IEC timer and learn what the instance data block stores.
Keep a fan running for four seconds after the motor stops using the off-delay timer's Q output.
Count parts to a preset of five with a count-up counter and clear it with the reset input.
Copy an operator speed word to the drive command word and see what MOVE does and does not calculate.
Turn a temperature value into hot and cold lamps with strict comparisons and check the limit value itself.
Reset a counter once when a mode switch turns on instead of holding it in reset while the switch stays on.
See why two pumps need two timer instances, and how an FB's instance data block differs from an FC.
Drive an open lamp with LD and a closed lamp with LDI from one gate limit switch.
Build a start/stop seal-in from LD, OR and ANI and check what happens when both buttons are held.
Fix a program that drives one output from two OUT rungs by joining the conditions in a single rung.
Latch an alarm with SET, clear it with RST and decide the winner when both rungs are true.
Turn a three-second delay into the right K value and read the timer contact to drive the pump.
Count five parts with a counter coil and clear it with a separate RST rung.
Load a speed preset into a data register and copy it to a second register.
Produce above, equal and below results for a count compared with a target of fifty.
Build a single-scan pulse from a memory relay and latch it to prove the press happened.
Scale a tenths-of-a-degree reading to whole degrees and see why integer division drops the fraction.
Check that a pressure sits between two limits using one flag per limit and an AND.
Delay a pump start by three seconds and see why the output must come from Q, not from the request.
Keep a fan on for four seconds after the motor stops and measure the run-on.
Sound a horn for exactly two seconds however long the button is held.
Latch a stop event on the falling edge of a running signal instead of on the level.
Count five parts into a box and clear the count with the reset input.
Track cars in a three-space car park with one up-down counter.
Give each of two production lines its own counter instance so the counts stay separate.
37 of the units are graded or interactive practice on simulated equipment rather than reading:
- Allen-Bradley: XIC: examine a bit for 1: Read a BOOL tag as a normally open contact and combine two of them in series to build a permit.
- Allen-Bradley: XIO: examine a bit for 0: Use the normally closed contact so a fault bit blocks a rung, and see why the fault logic reads the opposite way to the wiring.
- Allen-Bradley: OTE: the output that is rewritten every scan: Learn why an OTE drops with its rung, and fix the duplicate-OTE bug where the last rung scanned silently wins.
- Allen-Bradley: OTL and OTU: latch and unlatch a bit: Hold an alarm bit on after the trigger has gone and clear it only with a deliberate unlatch rung.
- Allen-Bradley: TON: the on-delay timer and its done bit: Start a pump three seconds after a request and read the timer's done bit instead of the request itself.
- Allen-Bradley: TOF: keep an output on after the rung drops: Run a cooling fan on for a fixed time after the motor stops, using the off-delay timer's done bit.
- Allen-Bradley: CTU: count rung transitions to a preset: Count five parts into a box with a count-up counter and clear it with a separate reset.
- Allen-Bradley: ONS: act once per press, not once per scan: Toggle a light once per push-button press by turning the button level into a single-scan pulse.
- Allen-Bradley: GRT and LES: compare two values in a rung: Turn a tank level into high and low lamps with strict greater-than and less-than limits.
- Siemens: Contacts: A and AN in STL, open and closed in LAD: Combine a normally open selector with a normally closed interlock, and read the same logic in STL.
- Siemens: The = coil: assign a result every scan: Merge two alarm conditions into one assignment instead of writing the same output twice.
- Siemens: S and R: set and reset a bit: Latch a motor with S and R and decide who wins when both conditions are true, using statement order.
- Siemens: TON in TIA Portal: PT, ET and Q: Delay a pump start with an IEC timer and learn what the instance data block stores.
- Siemens: TOF in TIA Portal: run-on after the input drops: Keep a fan running for four seconds after the motor stops using the off-delay timer's Q output.
- Siemens: CTU in TIA Portal: CU, R, PV and Q: Count parts to a preset of five with a count-up counter and clear it with the reset input.
- Siemens: MOVE: copy a value from one address to another: Copy an operator speed word to the drive command word and see what MOVE does and does not calculate.
- Siemens: Compare blocks: ==, <>, >, >=, <, <=: Turn a temperature value into hot and cold lamps with strict comparisons and check the limit value itself.
- Siemens: P_TRIG and R_TRIG: detect a rising edge: Reset a counter once when a mode switch turns on instead of holding it in reset while the switch stays on.
- Siemens: FB, FC and DB: where memory lives: See why two pumps need two timer instances, and how an FB's instance data block differs from an FC.
- Mitsubishi: LD and LDI: start a rung open or closed: Drive an open lamp with LD and a closed lamp with LDI from one gate limit switch.
- Mitsubishi: AND, ANI, OR, ORI: series and parallel contacts: Build a start/stop seal-in from LD, OR and ANI and check what happens when both buttons are held.
- Mitsubishi: OUT: the coil and the double-coil mistake: Fix a program that drives one output from two OUT rungs by joining the conditions in a single rung.
- Mitsubishi: SET and RST: latch a device on and off: Latch an alarm with SET, clear it with RST and decide the winner when both rungs are true.
- Mitsubishi: OUT T: timers that count in 100 ms steps: Turn a three-second delay into the right K value and read the timer contact to drive the pump.
- Mitsubishi: OUT C: counters, presets and RST: Count five parts with a counter coil and clear it with a separate RST rung.
- Mitsubishi: MOV: load and copy data registers: Load a speed preset into a data register and copy it to a second register.
- Mitsubishi: CMP: above, equal or below in one instruction: Produce above, equal and below results for a count compared with a target of fifty.
- Mitsubishi: PLS: one scan of output per rising edge: Build a single-scan pulse from a memory relay and latch it to prove the press happened.
- CODESYS and IEC 61131-3: IEC data types: BOOL, INT, DINT, REAL and TIME: Scale a tenths-of-a-degree reading to whole degrees and see why integer division drops the fraction.
- CODESYS and IEC 61131-3: Comparison: GT, GE, EQ, LE, LT and NE: Check that a pressure sits between two limits using one flag per limit and an AND.
- CODESYS and IEC 61131-3: TON in CODESYS: IN, PT, Q and ET: Delay a pump start by three seconds and see why the output must come from Q, not from the request.
- CODESYS and IEC 61131-3: TOF in CODESYS: Q holds after IN falls: Keep a fan on for four seconds after the motor stops and measure the run-on.
- CODESYS and IEC 61131-3: TP in CODESYS: a fixed-length pulse: Sound a horn for exactly two seconds however long the button is held.
- CODESYS and IEC 61131-3: R_TRIG and F_TRIG: edges, not levels: Latch a stop event on the falling edge of a running signal instead of on the level.
- CODESYS and IEC 61131-3: CTU in CODESYS: CU, RESET, PV, Q and CV: Count five parts into a box and clear the count with the reset input.
- CODESYS and IEC 61131-3: CTUD: count up, count down, QU and QD: Track cars in a three-space car park with one up-down counter.
- CODESYS and IEC 61131-3: Function block instances keep their own memory: Give each of two production lines its own counter instance so the counts stay separate.
Who this track is for
Technicians and students who work with, or are about to move to, more than one PLC brand and want each vendor's instructions explained in its own terms.
4 of the 37 units are free with a free account, with no card and no expiry. The other 33 are part of a paid plan; compare them on the pricing page.
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Are PLC instructions the same across Allen-Bradley and Siemens?
The concepts are shared, such as contacts, coils, timers and counters, but names, addressing, data types and execution rules differ. A direct translation can compile and still behave differently, so verify each instruction against the vendor documentation.
Do I need to learn every PLC brand?
No. Learn the underlying logic on one platform, then learn how the second platform names and organises the same ideas. Employers mostly want the transferable skill plus willingness to learn their brand.
Is this vendor software or a vendor emulator?
No. It teaches vendor-style syntax in a browser simulator. It is not vendor firmware and not a replacement for the manufacturer programming software.
How much of Vendor References is free?
4 of the 37 units are free with a free account, no credit card and no expiry, starting with Allen-Bradley: XIC: examine a bit for 1. The remaining 33 units are included with a paid plan; see the pricing page for the current plans.
Do I need a PLC or any hardware?
No. Everything runs in the browser against simulated equipment. It is training material: it does not replace supervised practice on real equipment, and lockout/tagout and a qualified person are required for real equipment.
Start with the free units
Browser-based, no install, no hardware.
Start free: Allen-Bradley: XIC: examine a bit for 1