pyrung 0.2.2

Write ladder logic in Python. Simulate it. Test it. Deploy it -- Currently targets AutomationDirect CLICK PLC and CircuitPython ProductivityOpen P1AM-200.

pyrung

Write ladder logic in Python. Simulate it. Test it. Deploy to Click PLCs or P1AM-200 hardware.

pyrung turns Python's with block into a ladder rung — condition on the rail, instructions in the body.

from pyrung import Bool, PLCRunner, Program, Rung, out

Button = Bool("Button")
Light = Bool("Light")

with Program() as logic:
    with Rung(Button):
        out(Light)

runner = PLCRunner(logic)
with runner.active():
    Button.value = True
    runner.step()
    assert Light.value is True

• Documentation: https://ssweber.github.io/pyrung/
• LLM docs index: https://ssweber.github.io/pyrung/llms.txt

Why?

AutomationDirect Click PLCs have no built-in simulator. You write logic, download it to hardware, and hope. pyrung lets you test first — same tag names, deterministic scans, real assertions. When it works, encode it with pyrung_to_ladder() and paste via clicknick.

Or skip the Click editor entirely — generate a CircuitPython scan loop for a ProductivityOpen P1AM-200 and run your tested logic on open hardware.

Or run your logic as an emulated Click over Modbus to test send/receive, no hardware required. You can even spin up two pyrung programs and test them talking to each other.

Quick start

# Requires Python 3.11+
uv add pyrung

A motor with start/stop logic

from pyrung import Bool, Program, Rung, latch, reset

Start = Bool("Start")
Stop = Bool("Stop")
Running = Bool("Running")

with Program() as logic:
    with Rung(Start):
        latch(Running)
    with Rung(Stop):
        reset(Running)

Test it

from pyrung import PLCRunner

runner = PLCRunner(logic)
with runner.active():
    Start.value = True
    runner.step()
    assert Running.value is True

    # Release start — motor stays latched
    Start.value = False
    runner.step()
    assert Running.value is True

    Stop.value = True
    runner.step()
    assert Running.value is False

Map to Click hardware when you're ready

from pyrung.click import TagMap, x, y

mapping = TagMap({
    Start:   x[1],    # Physical input  → X001
    Stop:    x[2],    # Physical input  → X002
    Running: y[1],    # Physical output → Y001
})

mapping.validate(logic)                # Checks against Click constraints
mapping.to_nickname_file("motor.csv")  # For Click programming software

What's included

Core engine

Pure f(state) → new_state scan cycle with immutable snapshots. Coils, latches, timers, counters, branching, subroutines, structured tags, edge detection, and more. Built to match real Click behavior — no surprises when you move to hardware.

Click PLC dialect

Hardware address mapping, memory bank validation, Modbus instructions, and nickname file export. Run any program as an emulated Click over Modbus for integration testing.

CircuitPython dialect

Generate a self-contained CircuitPython scan loop from the same program you already tested. Targets the ProductivityOpen P1AM-200 with 35 supported I/O modules, SD-backed retentive storage, watchdog, Modbus TCP, and RUN/STOP control.

VS Code debugger

Step through scans rung by rung, set breakpoints, force tags, diff states, and time-travel through scan history.

Learn more

Core Concepts	Scan cycle, SystemState, tags, blocks
Instruction Reference	Full DSL reference
Tag Structures	UDTs, named arrays, cloning, block config
Runner Guide	Execution, time modes, history, fork
Testing Guide	Unit testing with deterministic time
Forces & Debug	Force values, breakpoints, time travel

Disclaimers

• Simulation is best-effort. pyrung models Click PLC behavior as closely as practical, but it is not a certified simulator. You are responsible for verifying your program on real hardware before production use.
• Modbus is unauthenticated. The emulated Click Modbus interface and CircuitPython Modbus TCP server listen on the network with no encryption or access control — standard for Modbus, but keep them off untrusted networks.