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.
Also see the general SPI protocol
write ports
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 line l, position p. l is the top 3 bits p is the bottom 5 bits of the data. |
0x12 | set contrast. |
0x13 | set backlight. |
0x14 | reinit LCD. |
0xf0 | change address. |
read ports
The spi_lcd board supports two read ports:
port | function |
---|---|
0x01 | identification string. (terminated with 0). |
0x02 | read eeprom (serial number). |
examples
A usage of the 0x01 port is to define custom characters. Here in a less verbose format:
82 01 40 # set CGRAM char 0 line 0 82 00 01 02 04 08 10 10 10 # define character 0 (7 bytes) 82 11 00 # move to home position 82 00 41 42 0 # print characters A B and our newly defined character.
read identification
read the identification string of the board. ('spi_lcd 1.3').
data sent | data recieved | explanation |
---|---|---|
0x83 | xx | select destination with address 0x82 for READ. |
0x01 | xx | identify |
xx | 0x73 | 's' |
xx | 0x70 | 'p' |
xx | 0x69 | 'i' |
xx | ... | etc. |
Send text to display
Display the string "Hello World!" (only the first 5 bytes of the string shown).
data sent | data recieved | explanation |
---|---|---|
0x82 | xx | select destination with address 0x82 for WRITE |
0x00 | xx | datastream |
0x48 | xx | 'H' |
0x65 | xx | 'e' |
0x6c | xx | 'l' |
0x6c | xx | 'l' |
0x6f | xx | 'o' |
xx | ... | etc. |
set cursor position
move to line 1, character 5:
data sent | data recieved | explanation |
---|---|---|
0x82 | xx | select destination with address 0x82 for WRITE |
0x11 | xx | port 0x11 = set cursor position. |
0x25 | xx | 0x25 = 001 00101 = line 1 position 5. |