LCD doesn't work properly after wakeup from Standby mode

[R. M.]

Posted on November 30, 2017 at 16:45

Hi All ,

I am using stm32f4 Discovery board and after I wakeup from standby mode ,everything works as expected except the LCD ,it only shows a white background and doesn't change .

I will start checking SDRAM first, but just checking if this is a known issue ?

[Tesla DeLorean]

Posted on November 30, 2017 at 16:55

Assuming the STM32F429I-DISCO?

Coming out of standby requires you to properly configure external devices, this may include devices that did not power down. Initialization code therefore needs to be robust. Check you can communicate with the ICs properly, and how the setting might be different in the cold vs warm restart cases. The back-light is hardwired, it is going to work regardless of if you configure the screen or memory properly.

Check the SDRAM initializes properly, and test it, this will give a quick indication if that is the root of the problem, or the configuration of the frame buffer, etc.

[R. M.]

Posted on December 01, 2017 at 11:47

Hi Clive ,

Thank you for your reply .

I actually use the stm32cubeMX for my board configurations ,so I assume all the external devices are properly configured ,and init is robust .

yes I know backlight is hardwired ,and its not my problem.

how can I check the SDRAM initilization ,you mean through SPI ? 

[Tesla DeLorean]

Posted on December 01, 2017 at 18:26

Through writing test patterns and verifying they work, for example..

[R. M.]

Posted on December 06, 2017 at 17:32

I have used 'BSP_SDRAM_WriteData' and 'BSP_SDRAM_ReadData' to read and write from SDRAM ,and it seems to work fine after I wakeup.

But now after wakeup if I perform a system reset ,the LCD works fine !!

In the reference manual ,it says that the wakeup from standby mode is exactly as power down reset ,so how come a system reset makes it work and not standby mode reset ?

[Tesla DeLorean]

Posted on December 06, 2017 at 18:05

External devices may not share the same async reset or power domains.

Code can behave adaptively based on a flag indicating the reset came out of STANDBY

[R. M.]

Posted on December 08, 2017 at 18:12

Clive One wrote:

External devices may not share the same async reset or power domains.

Code can behave adaptively based on a flag indicating the reset came out of STANDBY

My reset main only check for this pwr flag to clear it ,nothing else ,where else in code ?

also I noticed that after exciting the standby mode NRST  doesn't go Low ,is that right ?

in the datasheet the power circuit says that it should go low after exciting standby mode .