Spi lcd 1.3 protocol

Each transaction on the SPI bus starts with the address of the board. The spi_lcd board will ignore any transactions on the SPI bus that do not start with its own address.

After the address a single byte indicates the "port" on the board that the data is written to. The software can thus define 256 ports on each board.

Some ports just set a single value. So writing more than one byte to such a port is redundant. Other ports are logically a stream of bytes. So writing more than one byte is encouraged.

The spi_lcd board defines several ports.

port	function
0x00	display data.
0x01	write data as command to LCD.
0x10	any data clears the screen.
0x11	move the cursor to x, y. y is the top 3 bits, x is the bottom 5 bits of the data.
0x12	set contrast.
0x13	set backlight.
0xf0	change address.