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STM32H743II FMC + 8080 LCD spurious writes

Question asked by Piotr S on Apr 20, 2018
Latest reply on Apr 21, 2018 by Andrew Berry


I'm interfacing STM32H743II with 8080 parallel bus LCD. I configured FMC in CubeMX as LCD Interface with 16bit bus and A11 as R/S pin. However I've run into problem with writing commands/data into LCD. A single uint16_t write under 0x68000000 address results in 4 writes to memory, out of which first write is valid data, and rest are 0, as seen on logic analyser snapshot.

Write is performed by following code:

#define COMMAND_POINTER 0x68000000
#define DATA_POINTER 0x68001000


static uint16_t * command = (uint16_t *) COMMAND_POINTER;
static uint16_t * data = (uint16_t *) DATA_POINTER;


*command = ILI9341_SWRESET; //software reset

I also tried HAL_SRAM_Write_16b(), but result is the same.


These writes basically compile to strh (Store register halfword) instruction, and executing this single instruction causes 4 write accesses to LCD. After little investigation i noticed, that writes under incremented address, for example 0x68000002 causes valid data only in second write operation, write under 0x68000004 causes valid data only in third write and so on. It's like FMC tries to write whole 64bit memory block at once.

ICache and DCache are disabled, i tried to disable FMC write FIFO, but it doesn't change much. Needless to say this FMC behaviour throws off communication with LCD.


Am I not taking some detail into account? i would like to avoid bitbanging LCD signals or changing HW design.