Spi lcd 1.3 protocol
The addresses on the SPI bus are 7 bits wide. The lower bit specifies if the transaction is to be a read or a write. Write transactions have the lower bit cleared (0), read transactions have the lower bit set (1).
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.
|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.|
The spi_lcd board supports two read ports:
|0x02||read eeprom (serial number).|