ACC Traffic Light Intersection Scene

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BRIDGE WS URL: Run acc-modbus-bridge.js first, then click CONNECT

OUTPUTS Y

NS GreenNorth/South go

NS YellowNorth/South caution

NS RedNorth/South stop

EW GreenEast/West go

EW YellowEast/West caution

EW RedEast/West stop

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INPUTS X

Ped PB N/SCross E/W road (N.O.)

Ped PB E/WCross N/S road (N.O.)

Phase Status

Phase: —

Sequence Log

Open ACC PLC Simulator to link — or press RUN for standalone modeSCAN #0

TRAFFIC LIGHT INTERSECTION SCENE

Four-Way Intersection with Pedestrian Requests

A twilight four-way intersection with N/S and E/W signal heads, road markings, pedestrian crosswalks, and corner buildings. Two pedestrian push buttons allow walkers to request an extended green phase. This scene teaches timed sequence control — one of the most common patterns in industrial PLC programming.

I/O MAP

Address	Dir	Description
X1	IN	Ped button N/S — request extended N/S green
X2	IN	Ped button E/W — request extended E/W green
Y1	OUT	N/S Green light
Y2	OUT	N/S Yellow light
Y3	OUT	N/S Red light
Y4	OUT	EW Green light
Y5	OUT	EW Yellow light
Y6	OUT	EW Red light

FIVE STEPS TO PLC PROGRAM DEVELOPMENT

Use these five steps to develop your ladder program for this scene. Run standalone mode first to observe correct behaviour, then build and test your program in the ACC PLC Simulator.

STEP 1

Define the Task

A four-way intersection must cycle through standard traffic signal phases automatically. N/S and E/W traffic must never have green simultaneously — a critical safety interlock. Yellow phases warn before red. A brief all-red clearance interval separates opposing greens. Pedestrian buttons must extend the relevant green phase by 5 seconds when pressed.

STEP 2

Define the Inputs and Outputs

X1=Ped N/S (extends N/S green so pedestrians can cross E/W road), X2=Ped E/W (extends E/W green so pedestrians can cross N/S road). Y1=NS Green, Y2=NS Yellow, Y3=NS Red, Y4=EW Green, Y5=EW Yellow, Y6=EW Red. Critical: at all times at least one direction shows red. During all-red clearance, both Y3 and Y6 are ON.

STEP 3

Develop the Sequence of Operation

Six phases: (1) NS Green + EW Red (~20s). (2) NS Yellow + EW Red (3s). (3) All Red (1.5s). (4) EW Green + NS Red (~20s). (5) EW Yellow + NS Red (3s). (6) All Red (1.5s). Repeat. Pedestrian: X1 pressed → extend phase 1 by 5s. X2 pressed → extend phase 4 by 5s. Request made during wrong phase must be stored and honoured next cycle.

STEP 4

Develop the PLC Program

Use TON timers (T1–T6) for each phase duration. Use C bits to track which phase is active — only one should be ON at a time. Each T/DN bit advances to the next phase. For pedestrian extensions, latch a request bit and add extra time to the relevant timer when the correct green phase is active.

STEP 5

Test the Program

Connect the scene, press RUN, observe the cycle. Verify: correct output pairs for each phase; yellow appears briefly between each green change; N/S and EW are never both green; X1 during N/S green visibly extends it; X1 during EW green stores the request and extends N/S green next cycle.

What is the ACC Modbus Bridge?

Step 1 — Download the installer

Step 2 — Install Node.js (one-time)

Step 3 — Run the installer

Step 4 — Start the bridge

Step 5 — Connect this scene

Modbus Address Map — Traffic Light Intersection