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STM32F746BGT6 LCD TFT 7" flickering

Question asked by Tran Minh Cong on Apr 2, 2018
Latest reply on Apr 16, 2018 by T J

Dear every body,

I are using LCD TFT 7 inch 800x480  in our design with STM32F746BTG6 processor working at  200 MHz frequency.

We are using STemWin Library on RTOS operating system FreeRTOS - Market leading RTOS (Real Time Operating System) for embedded systems with Internet of Things extensions  with LTDC support.

GUIBuilder.exe software will generate gui data.

I are statically storing the required ARGB format in external SDRAM.

The data is loaded from SDRAM to LTDC (STM32F7 LCD Controller) using DMA2D and FMC interface (Flexible Memory Controller – Working at 200/2 MHz).


Timing LCD TFT 7 inch from datasheet: 

 About frequency in system:

- SDRAM: 100MHz, use same bus data 16bit with other device. Examples:nor flash.

/* Timing configuration for 100Mhz as SD clock frequency (System clock is up to 200Mhz) */
Timing.LoadToActiveDelay = 2;
Timing.ExitSelfRefreshDelay = 7;
Timing.SelfRefreshTime = 4;
Timing.RowCycleDelay = 7;
Timing.WriteRecoveryTime = 2;
Timing.RPDelay = 2;
Timing.RCDDelay = 2; 
sdramHandle.Init.SDBank = FMC_SDRAM_BANK1;

sdramHandle.Init.ColumnBitsNumber = FMC_SDRAM_COLUMN_BITS_NUM_9;
sdramHandle.Init.RowBitsNumber = FMC_SDRAM_ROW_BITS_NUM_13;

sdramHandle.Init.MemoryDataWidth = SDRAM_MEMORY_WIDTH;
sdramHandle.Init.InternalBankNumber = FMC_SDRAM_INTERN_BANKS_NUM_4;
sdramHandle.Init.CASLatency = FMC_SDRAM_CAS_LATENCY_2;
sdramHandle.Init.WriteProtection = FMC_SDRAM_WRITE_PROTECTION_DISABLE;
sdramHandle.Init.SDClockPeriod = SDCLOCK_PERIOD;


sdramHandle.Init.ReadBurst = FMC_SDRAM_RBURST_ENABLE;
sdramHandle.Init.ReadPipeDelay = FMC_SDRAM_RPIPE_DELAY_0;


- LTDC: 19.2 MHz.

PeriphClkInitStruct.PeriphClockSelection = RCC_PERIPHCLK_LTDC;
PeriphClkInitStruct.PLLSAI.PLLSAIN = 192;
PeriphClkInitStruct.PLLSAI.PLLSAIR = 5;
PeriphClkInitStruct.PLLSAIDivR = 2;


While I'm getting data in norflash, LCD have prolems is flickering.

I know that LTDC will gennerate data to LCD automatically after SDRAM refresh, isn't it?

What is solution to hold data on LTDC while other device use bus data of SDRAM (16 bit data)?

Can you tell me solutions to fix that bug, please?

Thank you so much!