Coil Elements

Coils are the output elements of a Ladder Diagram rung. They receive the power state from the rung's logic (the result of evaluating all contacts and blocks) and write a Boolean value to their assigned variable. The Autonomy Edge IDE supports six coil types, covering standard outputs, latching, and edge-triggered behavior.

Coil Types Overview

Type	Symbol	Behavior
Regular	`--( )--`	Writes the rung's power state to the variable
Negated	`--(/)--`	Writes the inverse of the rung's power state
Set (Latch)	`--(S)--`	Sets the variable to TRUE when energized; does not affect it otherwise
Reset (Unlatch)	`--(R)--`	Sets the variable to FALSE when energized; does not affect it otherwise
Rising Edge	`--(P)--`	Sets the variable TRUE for one scan on a rising power edge
Falling Edge	`--(N)--`	Sets the variable TRUE for one scan on a falling power edge

All coils require a BOOL variable. Assigning a non-BOOL variable or an undefined name highlights the coil in red.

Regular Coil

The Regular coil is the most common output type. It directly reflects the power state of the rung:

Rung is energized (power reaches the coil) → variable is set to TRUE
Rung is de-energized (power does not reach the coil) → variable is set to FALSE

Key characteristic: The variable is updated every scan cycle. It follows the rung state in real time.

Example. Direct output:

alarm_light mirrors sensor_active. When the sensor is active, the light is on. When the sensor is inactive, the light is off.

Example. AND logic with regular coil:

motor_run is TRUE only when both conditions are met simultaneously.

Negated Coil

The Negated coil writes the inverse of the rung's power state:

Rung is energized → variable is set to FALSE
Rung is de-energized → variable is set to TRUE

Use case: Creating inverted outputs without needing a separate rung with a normally closed contact.

Example. Inverted status:

system_ok is TRUE when system_fault is FALSE, and vice versa. This is equivalent to:

Both approaches produce the same result. The negated coil approach is more compact.

Set Coil (Latch)

The Set coil is a latching output. When the rung is energized, it sets the variable to TRUE and leaves it there. When the rung is de-energized, the coil does nothing. The variable retains its current value.

Rung energized → variable = TRUE
Rung de-energized → variable unchanged (stays at its current value)

Key characteristic: Once set, the variable stays TRUE until explicitly reset by a Reset coil or by other logic.

Use case: Latch/unlatch pairs for motor control, alarm memory, and any situation where you need to "remember" that a condition occurred.

Example. Latching motor start:

Pressing start_button latches motor to TRUE. It stays TRUE even after start_button is released. Pressing stop_button resets motor to FALSE.

Reset Coil (Unlatch)

The Reset coil is the counterpart to the Set coil. When the rung is energized, it forces the variable to FALSE. When de-energized, it does nothing.

Rung energized → variable = FALSE
Rung de-energized → variable unchanged

Use case: Always paired with a Set coil to create a latch/unlatch circuit.

Example. Emergency stop with latch/unlatch:

running is latched TRUE when run_command is active and no fault exists. It is reset (unlatched) by either e_stop or fault.

Set/Reset Priority

When a Set and a Reset for the same variable are both energized in the same scan, the last one evaluated wins (since rungs execute top to bottom). In the example above, if both run_command and e_stop are TRUE simultaneously, the Reset in Rung 2 executes after the Set in Rung 1, so running ends up FALSE. This is the desired "stop has priority" behavior. To get "start has priority," place the Set rung below the Reset rung.

Rising Edge Coil

The Rising Edge coil produces a single-scan pulse when the rung transitions from de-energized to energized.

Rung transitions from de-energized to energized → variable = TRUE for one scan
All other conditions → variable = FALSE

Use case: Generating trigger pulses from sustained conditions, one-shot event signaling.

Example. One-shot pulse from level signal:

notify_pulse goes TRUE for exactly one scan when process_complete transitions to TRUE. Even if process_complete stays TRUE for many scans, notify_pulse is only TRUE once.

Falling Edge Coil

The Falling Edge coil produces a single-scan pulse when the rung transitions from energized to de-energized.

Rung transitions from energized to de-energized → variable = TRUE for one scan
All other conditions → variable = FALSE

Use case: Detecting when a process ends, counting deactivation events.

Example. Detect process end:

cycle_ended pulses TRUE for one scan when cycle_active drops from TRUE to FALSE.

Changing Coil Type in the IDE

To change a coil's type:

Double-click the coil element on the rung.
A dialog appears with six options: Default, Negated, Set, Reset, Rising Edge, Falling Edge.
Select the desired type.
The coil's visual symbol updates immediately.

The variable assignment is preserved when you change types.

Multiple Coils on a Rung

A single rung can drive multiple coils:

Both output_1 and output_2 receive the same power state. However, for clarity, it's usually better to use separate rungs or have a single output per rung.

What's Next?

Learn how to use function blocks within ladder rungs: Function Blocks in LD.