FB_PWM (Function Block)

Generates a pulse-width modulated (PWM) signal.

The output switches between Amplitude and 0 at a fixed Period. DutyCycle controls the proportion of the period the output is high, as a value between -1 and 1.

For example, a duty cycle of 0.3 produces a high output for 30% of the period and a low output for the remaining 70%. A duty cycle of -0.3 inverts this, producing a low output for 30% and a high output for 70%.

A duty cycle of 0 keeps the output permanently low. A duty cycle of ±1 keeps it permanently high.

Phase shifts the wave horizontally in radians. Negative values shift in the opposite direction. Bias shifts the output vertically.

Note

The block is FINAL and must be instantiated, not extended. Use FB_init to set tPeriod, fAmplitude, fBias, and fDutyCycle at declaration time.

Extends: FB_PeriodicSignal

Properties

DutyCycle

Type: LREAL

Gets or sets the duty cycle as a value between -1 and 1.

This controls the proportion of the period the output is high. A value of 0.3 keeps the output high for 30% of the period. A negative value inverts the wave — -0.3 keeps the output low for 30% and high for the remaining 70%. Values outside -1..1 are clamped. Changes take effect immediately.

IsHigh

Type: BOOL

Gets whether the output is currently in its high state.

TRUE regardless of the values of Amplitude, Bias, or Phase.

Methods

FB_init

Inputs

Name	Type	Description
`bInitRetains`	`BOOL`	if TRUE, the retain variables are initialized (warm start / cold start)
`bInCopyCode`	`BOOL`	if TRUE, the instance afterwards gets moved into the copy code (online change)
`tPeriod`	`LTIME`	Duration of one full cycle.
`fAmplitude`	`LREAL`	High-state output level. Low state is always 0.
`fBias`	`LREAL`	Shifts the output vertically.
`fDutyCycle`	`LREAL`	Proportion of the period the output is high. Clamped to -1..1.

Reset

Restarts the wave from the beginning by resetting the accumulated time to zero. The duty cycle, phase, amplitude, and bias are unaffected.

Run

Advances the PWM signal by one time step.

Note

Must be called once per cycle on a single PLC task. If the measured cycle time is zero or Period is zero, the method returns early without updating the output.