ctrl32

Ladder (LD)

Ladder (LD) on ctrl32

The ladder editor draws the logic the way an electrician reads a schematic: rungs between two power rails, contacts in series and in parallel, the coil at the right. Underneath there is no separate "ladder runtime" — every rung compiles into the same function blocks the FBD editor produces and the panel already executes. Uploading a ladder program is uploading data, never firmware.

A thermostat in ladder: BLINK heartbeat, a simulated temperature branch, hysteresis and the heating relay

Elements

Symbol Meaning
-[ ]- NO contact — conducts while the tag is TRUE
-[/]- NC contact — conducts while the tag is FALSE
-[P]- / -[N]- rising / falling edge (one cycle)
-( )- coil — the rung result lands in the tag
-(S)- / -(R)- set / reset latch
block in the rung TON, TOF, TP, CTU, CTD — the rung drives IN, Q carries on
box on the rung any block from the library with EN/ENO: while the rung conducts it executes, while it does not its state freezes and the outputs hold

Everything fits in ladder. Timers, counters, ramps, filters, comparators with hysteresis, PID, motor and valve blocks — every block sits in a rung as a box with the standard EN/ENO behaviour. The Toolbox offers them in the same groups as the block editor: Boolean, Math, Timers, Counters, General, Motion, CAN, GSM/GPS.

Blocks show their inner value at the right stub: a counter its CV, a timer its ET (elapsed), a blinker its REM (time left in the current phase). Bind it to a tag, or just read it — in simulation and during online monitoring every stub variable carries its live value on the line above it.

Series contacts AND together; a parallel branch ORs. The classic start/stop seal-in is exactly:

|--[ start ]--+--[/ stop ]-----------------( run )--|
|--[ run   ]--+

A rung does not need a coil

A new rung starts as a bare arrow — no wire across, no coil. Build it from either end:

  • add contacts and finish with a coil — the classic rung;
  • or put blocks on the rail: a box on a rung with no coil executes every cycle (a drawn TRUE contact in front of it says so), and the run wire simply ends in an arrow. Contacts placed before the boxes become their EN condition — no helper variable needed.

Working with rungs

  • + Rung adds a rung; click a contact, box or the coil to change its tag (with a filter), its kind, insert contacts before/after, add a parallel branch or another box. Right-click offers cut/copy/paste for elements, boxes and whole rungs, and insert rung above/below. Everything is undoable.
  • The comment line above every rung is written directly on the canvas — click it and type, multiple lines welcome, click away to keep it. The same text is the network comment in the block-diagram view.
  • Selecting a rung highlights it with a quiet grey background; the palette then targets that rung.
  • A (S) and (R) pair on the same tag becomes ONE flip-flop; the pair's order decides the priority (set-first = set wins).
  • Two plain coils on one tag are refused at the desk — the last writer would silently win on the panel. Use a branch or S/R.
  • Every contact and coil shows its variable name and, underneath, the tag's description as a //comment (edited right in the element popup; the comments checkbox hides them when the rungs should pack tighter). Descriptions travel with the project.
  • In test mode the rungs show the live power flow: conducting wires, symbols and block frames turn green — the frame as thick as the wires, so the active path reads at a glance. Clicking a contact toggles its tag (simulation only; connected to a panel everything is read-only).

Ladder and FBD — one owner, two views

A program belongs to ONE editor at a time. A ladder-owned program opens in the block editor as a read-only view — its networks mirror the rungs one to one, comments included — and a single button takes the ownership over when you want to continue in FBD. The way back is the same button on the other side. Nothing edited in one view can be silently overwritten by the other.

A function block created from a POU can be drawn in ladder too: its input and output ports behave as ordinary variables — contacts on the inputs, the coil on an output (see composite blocks).

Limits

32 rungs per program, 8 parallel branches per fork, one coil column. The block budget is shared with the whole program — 512 blocks per project (see limits); the Resources panel shows the consumption as you build.

Tags