> For the complete documentation index, see [llms.txt](https://px4.gitbook.io/px4-user-guide/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://px4.gitbook.io/px4-user-guide/development/concept/pwm_limit.md).

# PWM limit state machine

The`PWM_limit State Machine` controls PWM outputs as a function of pre-armed and armed inputs. Provides a delay between assertion of "armed" and a ramp-up of throttle on assertion of the armed signal.

## Quick Summary

**Inputs**

* armed: asserted to enable dangerous behaviors such as spinning propellers
* pre-armed: asserted to enable benign behaviors such as moving control surfaces
* this input overrides the current state
* assertion of pre-armed immediately forces behavior of state ON, regardless of current state
* deassertion of pre-armed reverts behavior to current state

**States**

* INIT and OFF
  * pwm outputs set to disarmed values.
* RAMP
  * pwm outputs ramp from disarmed values to min values.
* ON
  * pwm outputs set according to control values.

## State Transition Diagram

![PWM Limit state machine diagram](/files/lYqeAtrBsUMlzReBiI9R)