The LEDs module contains the C part of the MicroUI implementation which manages LED devices. This module is composed of two elements:

  • the C part of the MicroUI LEDs API (a built-in C archive),
  • an implementation of a low level API for the LEDs (LLLEDS) which must be provided by the BSP (see LLLEDS: LEDs).


The LEDs module provides only one implementation which exposes some low level API (LLLEDS) that allow the BSP to manage the LEDs. This implementation of the MicroUI Leds API provides some low level API. The BSP has to implement these LLAPI, making the link between the MicroUI C library leds and the BSP LEDs drivers.

The LLAPI to implement are listed in the header file LLLEDS_impl.h. First, in the initialization function, the BSP must return the available number of LEDs the board provides. The others functions are used to turn the LEDs on and off.

The LLAPI are the same for the LED which is connected to a GPIO (0 or 1) or via a PWM. The BSP has the responsibility of interpreting the MicroEJ Application parameter intensity.

Typically, when the LED is connected to a GPIO, the intensity “0” means “OFF,” and all others values “ON.” When the LED is connected via a PWM, the intensity “0” means “OFF,” and all others values must configure the PWM signal.

The BSP should be able to return the state of an LED. If it is not able to do so (for example GPIO is not accessible in read mode), the returned value may be wrong. The MicroEJ Application may not be able to know the LEDs states.

When there is no LED on the board, a stub implementation of C library is available. This C library must be linked by the third-party C IDE when the MicroUI module is installed in the MicroEJ Platform.



LEDs is a sub-part of MicroUI library. When the MicroUI module is installed, the LEDs module must be installed in order to be able to connect physical LEDs with MicroEJ Platform. If not installed, the stub module will be used.

In the platform configuration file, check UI > LEDs to install LEDs.


The MicroUI LEDs APIs are available in the class ej.microui.led.Leds.