Change Level of Backlight-Signal for "Backlight off/ScreenOff"?

  • Dear Support-Team,

    We use the efusA9X board with CE7 and currently migrate to WEC2013. When setting the system power state to "ScreenOff", CE7 sets the backlight signal BL_CTRL (PWM backlight dimming) to constant low and VCFL_ON (backlight on) to low. In this case the display becomes dark as expected. Everything is fine so far.

    The display mode is mode 9. We use only BL_CTRL, VCFL_ON is not connected.

    For WEC2013 the behavior of the backlight PWM signal BL_CTRL seems to have been changed. In opposite to CE7 the level of BL_CTRL becomes constant HIGH in "ScreenOff" power state instead of LOW. Thus the display stays bright. (VCFL_ON changes to low, but - as mentioned - we do not use this signal).

    ndcucfg's "backlight off/on" has no effect in WEC2013, dimming via changing the contrast works.

    Is this change a bug or a feature? :-)

    Is it possible to change the behavior of BL_CTRL so that it is constant low as it was in CE7 instead of being high when in power state "ScreenOff"?

    Is there a registry value, an ExtEscape sequence, a driver parameter or any other hack that allows to change this behavior?

    Best regards,


  • Hello,

    i have to check the code an will come back asp but I wonder that there is a difference between WEC7 and WEC2013.

    >>Is this change a bug or a feature?

    << Note, there are some displays which have max. brightness with duty cycle 0% and other with duty cycle 100%! So specific value on BL_CTRL does not clearly define the brightness of any display.

    F&S Elektronik Systeme GmbH
    As this is an international forum, please try to post in English.
    Da dies ein internationales Forum ist, bitten wir darum, Beiträge möglichst in Englisch zu verfassen.

  • After updating WEC2013 and the BSP/PRJ to the current versions the display becomes dark again when switching into power state "screenoff". What not works is switching off the backlight via ndcucfg, but this is not required for my project. So from my side no further actions are required. To summarize the current situation:

    • Power state "screenoff": Both signals BL_CTRL (PWM backlight dimming) and VCFL_ON (backlight on) gets stable low => display is off
    • "Backlight off" via ndcucfg: BL_CTRL (PWM backlight dimming) is not changed, VCFL_ON (backlight on) gets stable low => in my project the display remains on.