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Running the circuit
What happens when you press Simulate, how to control the speed of time, and why the editor locks while the circuit is live.
Press Simulate in the top bar. The button turns into Running, and from that moment the sheet is a live machine: push buttons can be pressed, contacts change state, motors turn, the PLC scans its program.
Press Stop Simulation to go back to Design Mode.
What changes while it runs
| Design Mode | Running | |
|---|---|---|
| Place, move, wire, delete | yes | no |
| Press buttons, turn selectors, operate the plant | no | yes |
| Auto-save | on | off, on purpose |
A test run never overwrites your drawing
Auto-save is disabled during simulation. Whatever you do while the circuit is live — trip a breaker, blow a fuse, drive a tank to overflow — the saved project is still the one you designed.
If a tool looks disabled, the mode is the first thing to check. The editor says it plainly: "Stop simulation first".
The speed of time
Next to the Simulate button there is a Simulation speed pill, from ×0.2 to ×10.
It does not speed up "the animation" — it multiplies time for the whole system at once. A 30-second timer, the heating of a thermal relay and a tank filling all age together, so nothing ever drifts out of step with anything else. It is a fast-forward of the film, not of one actor.
A real PLC keeps its own clock
If you drive the circuit from a real CPU through the UnifCAD bridge, its timers run in real time. Someone else's clock cannot be fast-forwarded. The ×N on the pill is telling you the difference.
Watching two modules at once
Split View puts two modules side by side — typically the Schematic and the Programming editor — so you can watch a rung go true and the contactor pull in at the same time. Two panes maximum; drag a module onto a pane to replace it.
This is the fastest way to debug a program: the answer to "why did the motor not start?" is almost always visible in the other pane.
It keeps running in the background
A running simulation does not pause when you look away. Go to another tab to check a datasheet and the process carries on: the tank keeps filling, the timer keeps counting, the motor keeps turning.
On a very large project the simulation may stretch its scan cycle to keep up, and it tells you so: "Scan cycle increased to … ms — large project". That is information, not an error — the same thing a real CPU reports as scan time.