Virtual Simulation¶

PiPLC includes a complete virtual I/O simulation environment for testing programs without physical hardware.

Simulation Panel¶

In simulation mode, the SimulationPanel provides:

• Toggle inputs: Click to activate/deactivate inputs
• Force bits: Manual override of any I/O/B address
• Memory monitor: View values in real time
• Watch panel: Add specific variables for monitoring

Starting a Simulation¶

1. Press ++f5++ to start simulation
2. Use the simulation panel to toggle inputs
3. Press ++f6++ to pause, ++f7++ to stop

Forcing I/O¶

To force a value during simulation:

1. Right-click on a contact or coil
2. Select Force ON, Force OFF, or Unforce
3. Forced bits override the normal scan cycle
4. A force bitmap tracks all forced addresses

Force semantics (IEC 61131-3 / CODESYS style)¶

PiPLC follows the IEC 61131-3 / CODESYS model rather than the Allen-Bradley split:

• Forcing overrides the variable, not just the physical I/O. Every reader — contacts, the engine, the UI, HMI — sees the forced value uniformly.
• While a bit is forced, writes by ladder logic are silently suppressed for that address. An OTE driving O:0/2 cannot change the bit while it is forced; the rung still evaluates and the visual still reflects power flow through the rung, but the underlying bit stays at the forced value.
• Unforcing removes the override. The next normal write (an OTE on a true rung, an input scan, MOV, HMI, etc.) overwrites the bit as usual.

Sub-element addresses (timer/counter bits like T:5.DN) are not force-addressable — only direct bit addresses in the I:, O:, and B: regions can be forced.

Force indicator badge¶

Any contact or coil whose underlying bit is currently forced shows a small colored F badge to the left of the address text:

• Green badge — the bit is forced to 1 (ON)
• Black badge (default) — the bit is forced to 0 (OFF)

The badge colors are configurable in Preferences → Colors → Force Indicator. The badge appears on every visual instance of the forced address — XIC, XIO, OTE, OTL, OTU — so you can spot at a glance which signals you currently have under manual override.

Coil visual state vs. rung power¶

A subtle but important detail: the lit / unlit state of a coil (OTE/OTL/OTU) reflects the underlying bit value, not the rung's power flow. This matters in three common cases:

• An OTL that latched on an earlier scan stays lit even when the rung that latched it goes false — because the bit itself is still 1.
• A forced coil shows the forced value regardless of whether the rung is feeding power to it.
• A coil whose address is written by HMI / Modbus / SCRIPT shows whatever external clients wrote, not what the rung last computed.

The wire passing through the coil still tracks rung continuity in the usual way; only the coil glyph itself reflects the bit.