LPC1788 external SDRAM for LCD Frame buffer

[lorenzogalbiati]

Hello,

for a commercial product in my factory I need to use LPC1788 and LCD controller to drive a 320x240 TFT display.

This is the first time I use both of them, I have always used small display with on-board SPI or parallel controller and I have some big questions because I don't know what to do.

I've read the LCD frame buffer must be placed on an external SDRAM because internal peripheral RAM is too small to store it.

What kind of SDRAM? My LPC1788 package (144pin) has only 8 bit data bus for EMC; is it necessary to use a bigger package to have 32bit SDRAM? What could be the drawback by using 8bit SDRAM?

If I use only 4 colors (2bit per pixel) can I use only internal peripheral ram?

Many thanks for your help? 

Best regards

[lorenzogalbiati]

Dear EdwinHZ,

thanks for the answer. I understand; I have a little question. If I use a 8-bit color code in the palette (not full 24bit) I suppose using a 8bit SDRAM is OK because data base has the same length of the color code and every pixel is read with a single read cycle.

Is it correct?

Best regards

[EdwinHz]

Hi @lorenzogalbiati,

Yes, this is correct.

BR,
Edwin.

[EdwinHz]

Hi @lorenzogalbiati,

The recommendation to place the LCD frame buffer on an external SDRAM is mainly because the size of the frame buffer usually ends up being quite large, and the frame buffer alone would end up spending quite a large percentage of space. The external SDRAM doesn't necessarily have to be a specific type, as long as it can reliably store and transmit the frame buffer.

That said, it is worth noting that using an 8bit SDRAM might present a bottleneck for the speed at which the frame buffer can be transmitted. Having this bottleneck might present an issue with the frames per second that can be achieved. In this case, the bigger package will definitely help. 

BR,
Edwin.