Practice Allen-Bradley ladder logic with RSLogix-style XIC, XIO, OTE, OTL, OTU, TON, and CTU instructions. Run any of ten machine scenarios in AB syntax from your browser. No Studio 5000 install.
There are three ladder-logic dialects that matter. The IEC 61131-3 standard is implemented by CoDeSys, OpenPLC, Beckhoff TwinCAT, and almost every non-AB, non-Siemens controller. Allen-Bradley (Rockwell) dominates North-American discrete-manufacturing plants; its instruction set (XIC, XIO, OTE) and addressing (I:0/0, O:0/0) will be what you see in most US factories. Siemens is dominant across Europe, with its own STL / TIA Portal conventions and %I0.0 addressing.
Pick AB if: your target job is in a North-American plant, you are taking a Rockwell certification, or your school uses RSLogix / Studio 5000. Pick Siemens if: you are in Europe, you are taking a Siemens SCE certification, or your plant runs S7-1200 / S7-1500. Pick IEC if: you want maximum portability across brands or you are learning the fundamentals and want to stay dialect-agnostic.
On this simulator you do not have to pick once. Every scenario accepts all three dialects, and you can switch between them on the same scenario to compare how an identical rung renders in each syntax. For AB specifically, the rest of this page covers syntax, a runnable sample, and a link into the editor.
AB ladder uses a compact three-letter mnemonic set descended from the original PLC-5 / SLC-500 instruction sets. The key ones to memorise:
XIC — examine if closed. A normally-open contact. Passes power when the tag is true.XIO — examine if open. A normally-closed contact. Passes power when the tag is false.OTE — output energise. The standard non-retentive coil.OTL — output latch. Sets the bit and leaves it set.OTU — output unlatch. Clears the bit.TON — on-delay timer. Takes a preset in milliseconds; read its done bit as .Q and elapsed time as .ET.CTU — count-up counter. Increments on rising edges of the input; read the accumulator as .CV and the done bit as .Q.Addresses follow the file-based convention: I:0/0 is the first bit of input file 0, slot 0. O:0/0 is the matching output. Bit file B3 holds internal memory bits. Timer and counter instances are declared by name with TAG; read a timer's done bit as T_Name.Q and its elapsed time as T_Name.ET, and a counter's accumulator as C_Name.CV. This file-based I/O style traces back to RSLogix 500 / MicroLogix / SLC-500.
Newer ControlLogix / CompactLogix platforms use tag-based addressing where you declare named tags in a tag database and reference them directly (Motor_Start, Conveyor_Run). Our simulator accepts both styles \u2014 use TAG directives in the source to declare tag-based addressing, or the I:/O: conventions for file-based.
This is the canonical Allen-Bradley three-wire seal-in rung. START is the momentary push-button (XIC, normally open). The rung latches via the MOTOR coil\u2019s own contact. STOP is wired as normally closed in the rung (XIO) so a broken wire fails safe.
// Classic 3-wire motor start / stop with seal-in.
// START is a momentary push-button; MOTOR latches via its own feedback
// contact until STOP (normally-closed in the rung) breaks the seal.
TAG START I:0/0 BOOL
TAG STOP I:0/1 BOOL
TAG MOTOR O:0/0 BOOL
XIC START OR XIC MOTOR AND XIO STOP OTE MOTORLoad the motor start-stop example in the editor and switch dialect to Allen-Bradley from the dialect toolbar. The sample above is already the golden fixture for that scenario\u2019s AB dialect test.
All ten scenarios accept Allen-Bradley syntax. These are the two we recommend starting with for AB-specific practice.
The classic seal-in rung. A fifteen-minute exercise in XIC, XIO, and OTE with a fault-handling branch you can build up.
Photo-eye sort station with CTU counters and a timed reject actuator. Good second scenario to practice counter and timer instructions in AB style.
No Studio 5000 install. No Rockwell license. Two scenarios free, no credit card.
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