Add ST7789 example

[Joe7M]

Hi Chris,

here a SPI example for a TFT with a ST7789 controller. In principal it works but it has two problems:

• extreme slow, because every pixel is send sequentially. It would be great, if SPI.write supports to send an array in one go. Every element of the array should be interpreted as a byte.
• Commands needs to be send as single bytes. Your current implementation only supports sending 2 bytes. Would be great to implement the possibility to send only one byte. Fortunately it works in this case, because the controller has a NOP command (dummy command), which can be send as the second byte. When sending one byte data, the second byte is set to 0 which luckily works, too.

It would be great, if for I2C these two thinks could also be implemented.

Best regards, Joerg

[chrisws]

Thanks for this. I have the TI educational booster pack mkII from a course I did a few years ago.

This has a ST7735S lcd. Hopefully it will be fairly similar to the ST7789.

It should be simple enough to add multi-byte handling to SPI.write. This is already implemented for the TWI interface.