Flickering and SDRAM speed

[lorenzogalbiati]

Hello,
I have a problem about flickering on a 320x240 TFT display connected to LPC1788 with an external SDRAM 16Mbit.
The maximum frequency of EMCLCK pin is 80MHz as indicated on LPC1788 datasheet and with this frequency the required time to fill the frame buffer is about 50ms while my VSYNC signal is 16ms.
These times have been measured with oscilloscope.
There is no time to prepare a new buffer during the VSYNC period, so "dual buffer" is impossible to obtain with LPC1788 because EMC frequency is limited.

Can anyone give me an hint or a solution? 
Best regards

[EdwinHz · Accepted solution]

Hi @lorenzogalbiati,

Driving a display is difficult on an LPC1788 due to the limitation that you mention. I would recommend upgrading to a LPC55s69 if possible, instead.

BR,
Edwin.

[lorenzogalbiati]

Dear Edwin,

thanks for the answer.

I agree this is a limited microcontroller; i've spent many hours to understand a different double buffer algorithm and I have developed a different version without the necessity to copy all the frame buffer (1.8Mbit): I change only a memory pointer, in this case with only few ns the buffer swap is done.

Results are eccellent, I move bitmap and graphic with fast speed withouy flickering.

Best regards.