I have a VM816C50A dev kit with 5" screen which I've hooked up to my XMOS processor via SPI and seems to be working apart from one thing. I've got the display initialised and drawn some text on the screen without any problems, but after a few seconds the screen gradually fades to white or blanks out. I can stop it doing this by writing the same screen to the BT816 once a second, but I'm obviously missing something really basic somewhere that describes how often and why you need to do this. I'd assumed (obviously wrongly), that once I'd written a screen to the BT816 it would stay on screen until I told it to draw something else.

Can somebody point me in the direction of what I'm missing please?