The LED module contains the C part of the MicroUI implementation which manages LED devices. This module is composed of only one element: an implementation of the Low Level APIs for the LEDs which must be provided by the BSP (see LLUI_LED: LEDs).

Functional Description

The LED module implements the MicroUI Leds framework. LLUI_LED specifies the Low Level APIs that receive orders from the Java world.

The Low Level APIs are the same for the LED which is connected to a GPIO (0 or 1), to a PWM, to a bus (I2C, SPI), etc. 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 other values “ON”. When the LED is connected via a PWM, the intensity “0” means “OFF”, and all other values must configure the PWM duty cycle 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 BSP has to save the LED state in a global variable. If not, the returned value may be wrong and the MicroEJ Application may not be able to know the LEDs states.

Low Level API

The LED module provides Low Level APIs that allow the BSP to manage the LEDs. The BSP has to implement these Low Level APIs, making the link between the MicroUI library and the BSP LEDs drivers.

The Low Level APIs to implement are listed in the header file LLUI_LEDS_impl.h. First, in the initialization function, the BSP must return the available number of LEDs the board provides. The other functions are used to turn the LEDs on and off.

MicroUI LED Low Level

Led Low Level API

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. This stub library does not provide any Low Level API files.



LEDs is a sub-part of MicroUI library. When the MicroUI module is installed, the LED 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.