Interface Tour

Layout of the main simulator window

Toolbar (top)

Zoom Controls

A − / 100% / + / 1:1 control cluster sits in the bottom-right corner of the ladder panel.

Left Panel — Instruction Palette

Click an instruction type to select it (it highlights in blue). Then right-click any contact on the ladder to insert the selected type before or after it. The address field pre-fills with the next available address for that type.

A ◀ collapse tab sits on the right edge of the palette. Click it to collapse the panel to a thin strip, giving the ladder more horizontal space. Click the ▶ tab again to restore it.

Centre — Ladder Canvas

The main programming area. Rungs are displayed as horizontal rails. In STOP mode, contact bars show bit state (green = energised). In RUN mode, powered wires and energised coils glow green.

• Double-click any element to open the Edit dialog.
• Double-click the rung header bar (the comment area) to edit the rung comment directly. A faint placeholder text appears on rungs with no comment.
• Right-click any contact for the context menu (insert, delete, add parallel branch).
• Drag the handle on the rung header (STOP mode only) to reorder rungs.
• Hover between rungs to reveal the Insert Rung strip.
• + button (STOP mode) appends a contact slot to the rung input area.

Right Panel — I/O Tabs

Seven tabs: I/O (used addresses summary), X, Y, C, T, CT, AN (analog). See the I/O Panel Tabs section for details.

A ▶ collapse tab sits on the left edge of the I/O panel. Click it to collapse the panel and give the ladder more space. Click the ◀ tab again to restore it.

Light / Dark Theme

Click the ☀ THEME button in the toolbar to switch between the default dark theme and a softer light theme. The button label changes to 🌙 THEME when light mode is active.

In the light theme, energised contacts and I/O indicators use a bright vivid green with a glow halo to ensure ON states remain clearly distinguishable from OFF states.

Status Bar (bottom)

Displays the current mode (RUN/STOP), contextual hints, and the system clock. After most actions a confirmation message appears here.

Quick Start

Get a rung running in under two minutes

1. Open acc-plc-simulator.html in any modern browser.
2. The default Start/Stop/Jog program loads automatically.
3. Press F5 (or click RUN) — the LED turns green and the scan begins.
4. On the X tab (right panel), click X1 to toggle the Start input ON — Y1 energises.
5. Click X1 again to release it — Y1 stays on (seal-in circuit).
6. Click X2 to pulse the Stop — Y1 de-energises.
7. Press F4 to stop the scan.

Adding Your First Rung

1. In STOP mode, hover near the bottom of the ladder until the ⊕ Add New Rung strip appears. Click it.
2. The Rung Template picker opens — choose XIC → OTE for a simple contact/output rung.
3. Double-click the new contact (address shown in amber) to open Edit. Change the address to X4 and click Apply.
4. Double-click the output coil and change its address to Y4.
5. Press F5 to run, then toggle X4 on the X tab to see Y4 energise.

Rungs & Editing

Creating, modifying, and organising rungs

Inserting a Rung

Hover between any two existing rungs to reveal the ⊕ Insert rung after XXXX strip, or hover below the last rung for ⊕ Add New Rung. Clicking opens the Rung Template Picker with pre-built patterns.

Deleting a Rung

Click the ✕ circle button on the top-right of any rung header. A confirmation dialog prevents accidental deletion.

Reordering Rungs

In STOP mode, drag the ⠿ handle on the left of the rung header to a new position. An amber drop-indicator line shows the insertion point.

Editing Elements

Double-click any element to open the Edit Instruction dialog. You can change the instruction type, address, preset value, and add a comment. You can also edit the rung comment from here.

Editing the Rung Comment

Double-click anywhere on the rung header bar (the row showing the rung number and comment text) to open the Edit Rung Comment dialog. Type the new comment and click Apply or press Enter. Leave the field blank and apply to clear the comment.

Rungs with no comment show a faint "double-click to add comment…" placeholder to make the feature discoverable.

Right-Click Context Menu

Rung Structure Rules

• Every rung must have at least one input contact and exactly one output element (coil or block) on the right rail.
• Input contacts are evaluated left-to-right; the result drives the output.
• Timer and counter blocks occupy the output position — wire continuation exits from their right side carrying the DN bit.

Contacts

Input-side bit-reading instructions

Address Examples

• X1 — Digital input 1
• Y3 — Digital output 3 (used as a contact to read back its state)
• C100 — Internal control relay 100
• T1/DN — Timer 1 Done bit
• T1/EN — Timer 1 Enable bit
• T1/TT — Timer 1 Timing bit
• CT1/DN — Counter 1 Done bit
• Bare T1 resolves to T1/DN automatically

In STOP Mode

Contact bars show the current bit state regardless of power flow. A green bar means the bit is 1. Wires remain dark — power flow is only shown in RUN mode.

Outputs

Output coil instructions — right-rail elements

Timers

TON and TOF — time-based control

Timer Parameters

• Address — T1 through T256
• Preset — time in milliseconds. 1000 = 1 second, 5000 = 5 seconds.
• Accumulator — counts up from 0 each scan (approximately 100 ms steps).

Timer Bits

Reset

Add a RES block (address T1) on a separate rung. When that rung is powered, Acc resets to 0 and DN clears.

Counters

CTU, CTD and RES — event counting

Counter Parameters

• Address — CT1 through CT256
• Preset — integer count target (no units)
• DN bit — CT1/DN or bare CT1

Analog I/O

AX inputs (0–4095) and AY outputs (0–4095)

The simulator supports 12-bit analog channels using 12-bit AX/AY registers. All values are integers in the range 0–4095, representing 0–10 V (or 4–20 mA in real hardware).

Analog Inputs — AX

Analog Outputs — AY

Analog Compare Instructions

Analog compare blocks sit in the input area of a rung and pass or block power flow on every scan based on the live AX register value versus the fixed comparand.

MOV — Move Value to AY

The MOV block occupies the output position. When the rung is powered it writes the Source value to the destination AY register. The source can be a constant (e.g. 2048) or an AX register (e.g. AX1).

Parallel Branches

OR logic — multiple paths to the output

A parallel group connects two or more contact paths in parallel. If any branch passes power the output is energised — this is Boolean OR logic.

Adding a Parallel Branch

• Right-click a contact and choose Add Parallel Branch. The contact is wrapped in a two-branch group; the new branch contains a default XIC contact.
• Or click the ‖+ button that appears below an existing parallel group in STOP mode.

Editing the Parallel Group

Right-click any contact in the group and choose Edit Parallel Group, or double-click the left rail of the group, to open the Parallel Branch Editor.

In the editor you can:

• Add/remove contacts within each branch (series AND logic inside a branch)
• Add new branches (more OR paths)
• Remove branches (minimum 2 required; removing down to 1 unwraps the group)

Series contacts inside a branch

Each branch can contain multiple contacts in series — all must be TRUE for that branch to pass power (AND logic within the OR group).

Memory Map

All addressable registers in the simulator

I/O Panel Tabs

Right-side panel — seven tabs for monitoring and forcing

Run / Stop / Step

PLC operating modes

STOP Mode

The PLC is halted. No scan cycle runs. All Y and C outputs are de-energised and AY registers are cleared. You can:

• Edit the program (add, move, delete rungs and elements)
• Toggle X inputs and C relays to preview contact states
• Force Y outputs ON/OFF via the Y tab or I/O tab
• Manually set AY values via the AN tab or I/O tab
• Execute a single scan with STEP — only available when no scene is connected

RUN Mode

The scan cycle executes every 100 ms. The ladder canvas shows live power flow (green = energised). Inputs from a connected scene update each scan. Editing is disabled in RUN mode.

STEP Mode

While in STOP mode and with no scene connected, press STEP to execute exactly one scan. Useful for tracing logic one step at a time without continuous scanning.

Scan Cycle

How the simulator executes your program each 100 ms

Execution Order

1. Rungs execute from Rung 0000 to the last rung, top to bottom.
2. Within each rung, elements are evaluated left to right.
3. Parallel branches: all branches are evaluated; the rung is powered if any branch is TRUE.
4. OTE outputs are cleared at the start of each scan; they are only set when their rung is powered.
5. OTL/OTU bits persist across scans — they only change when a latch/unlatch rung is powered.

Timing Resolution

The nominal scan interval is 100 ms. Timer accumulators increment by the actual elapsed time since the last scan (capped at 500 ms). The scan time counter in the toolbar shows the most recent execution time in milliseconds.

Forcing I/O

Manually overriding bit and register states

Forcing X Inputs

Click any X button on the X tab or I/O tab at any time (RUN or STOP). In RUN mode the forced value is used in the next scan immediately. In STOP mode it triggers a display refresh of contact states.

Forcing Y Outputs

Y bits can only be forced in STOP mode. Click the LED on the Y tab or I/O tab to toggle. The change propagates to a connected scene immediately via BroadcastChannel.

Forcing C Relays

Click any C button on the C tab or I/O tab at any time. Useful for simulating latch states or internal flags without having to construct a full rung to set them.

Forcing AX Analog Inputs

Drag the slider on the AN tab or I/O tab for any AX channel. The new value takes effect on the next scan in RUN mode, or updates contact comparisons immediately in STOP mode.

Forcing AY Analog Outputs

In STOP mode only, type a value (0–4095) into the AY input field on the AN tab or I/O tab and press Enter. In RUN mode the field is read-only — the program controls AY via MOV rungs.

Save & Load

Program storage — browser slots and JSON files

Saving

1. Click 💾 SAVE in the toolbar.
2. Type a name in the Program Name field.
3. Click Save — the program is stored in browser localStorage under that name.
4. If a slot with the same name already exists it is overwritten. Up to 10 slots are kept.

Loading

1. Click 📂 LOAD.
2. Click a slot to load it (confirmation required to prevent accidental overwrite).
3. Memory resets on load (X inputs retain state; Y, C, T, CT, AX, AY clear).

Auto-Restore

On page load the simulator automatically restores the most recently saved slot. No manual action is needed between sessions.

File Export / Import

In the Save/Load dialog, use ⬇ Export .json to download the program as a JSON file. Use ⬆ Import .json to load a previously exported file — useful for sharing programs between computers.

Rung Templates

Pre-built rung patterns for common tasks

When inserting a new rung the Rung Template Picker opens. Addresses are auto-filled with the next available address for each type — you will rarely need to edit them manually.

Connecting a 3D Scene

Linking the simulator to an interactive machine visualisation

3D Scenes are separate HTML files that display animated industrial machines. When connected to the simulator they exchange I/O state in real time via the browser's BroadcastChannel API — no server or network connection is needed.

How to Connect

1. Place the scene HTML file in the same folder as acc-plc-simulator.html.
2. Ensure acc-scenes.js is also in the same folder and lists the scene.
3. Click CONNECT in the simulator toolbar.
4. The Connect dialog lists all available scenes from acc-scenes.js.
5. Click LAUNCH ↗ next to the scene you want — it opens in a new browser window.
6. Once the scene loads, the CONNECT button changes to LINKED with a pulsing blue dot.
7. The connected scene name appears next to the button.

Disconnecting

Close the scene window. The simulator detects the loss of heartbeat messages within 2 seconds and resets the CONNECT button to its idle state.

Only One Scene at a Time

Only one scene can be connected simultaneously. If a scene is already linked, the LAUNCH buttons for other scenes are disabled (shown as BUSY). Close the current scene window before connecting a different one.

Standalone Scenes

Running a 3D scene without the simulator

Each scene HTML file is fully self-contained and can be opened directly in a browser without the simulator running. In standalone mode the scene operates as a 3D demonstration — you can interact with the machine but PLC logic is not executed.

Opening a Scene Standalone

1. Open the scene HTML file directly in your browser (e.g. acc-conveyor-scene.html).
2. The scene will initialise and display the machine in its default state.
3. Interact with the machine elements as designed (click buttons, observe animations).

Connecting the Simulator Later

With the scene already open in one window, open acc-plc-simulator.html in a second window. The scene will detect the simulator's presence via BroadcastChannel and link automatically — you do not need to re-open the scene.

Use Cases for Standalone Scenes

• Demonstrating machine operation without needing to explain ladder logic
• Exploring the 3D environment before writing the control program
• Classroom display on a projector while students write programs on their own machines

Scene I/O Mapping

Which signals are exchanged between the simulator and a scene

The BroadcastChannel (acc-plc-link) carries two message types each direction:

Scene → Simulator (Inputs)

Simulator → Scene (Outputs)

Scene I/O Chips

When you open the CONNECT dialog, each scene card shows coloured chips listing its specific I/O assignments — green chips are inputs to the simulator (from the scene), olive chips are outputs from the simulator (to the scene).

Keyboard Shortcuts

All keyboard shortcuts available in the simulator

Undo / Redo

The simulator maintains an undo history of up to 50 states. A snapshot is taken automatically before every edit operation, including:

• Inserting or deleting a contact
• Editing an instruction (address, type, preset, comment)
• Adding, editing, or removing parallel branches
• Inserting or deleting a rung
• Dragging rungs to reorder them

The ↩ UNDO and ↪ REDO buttons in the toolbar are greyed out when there is nothing to undo or redo. Loading a program (via LOAD or Import) and using CLEAR both reset the history to start fresh.

Address Reference

Complete syntax for all register types

Example Programs

Common ladder logic patterns

1 — Start / Stop / Seal-In (Motor Starter)

2 — Jog Circuit (no seal-in)

3 — On-Delay Timer (Fan delay)

4 — Analog Threshold (High-level alarm)

5 — Hysteresis Band (Heating control)