User Interface

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This is the documentation page for the RPi_UI board.


Assembly instructions


Possible Configurations

External resources


Additional software

Related projects


The 26 pin gpio connector is described at elinux
The SPI connector has the same pinout as the atmel 6-pin ICSP connector and is documented here: SPI_connector_pinout.
The I2C connector is documented here: I2C_connector_pinout.
The UART connector is documented here: uart connector pinout.


The only LED is a power indicator.

jumper settings

There is one 2x2 pin jumper (JP1), which controls which SPI bus (actually which SPI chip-select line) is routed to the AVRs slave-select pin, and which is routed to the reset pin (to enable reprogramming of the AVR):
Left pads/pins connected: SPI0 connected to Slave-Select Right pads/pins connected: SPI1 connected to RESET Bottom pads/pins connected: SPI0 connected to RESET Top (near the LCD) pads/pins connected: SPI1 connected to Slave-Select

There is also one solder jumper, SJ1, which controls the supply voltage on the SPI, I2C, and UART connectors:
1-2: 5V (left)
2-3: 3V3 (right, near the PCB edge)


To make the RPI_UI PCB do things, you need to send things over the SPI or I2C bus to the PCB. A comparison of the two protocols can be found here.

The general overview of the SPI protocol is here.

The software

Controlling the display works the same way as our SPI_LCD or I2C_LCD modules. Reading the pushbuttons is very much like the DIO module. The read and write ports are described below.

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 rpi_ui 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 rpi_ui board supports several read ports:

port function
0x01 identification string. (terminated with 0).
0x02 read eeprom (serial number).
0x20 read button 1
0x21 read button 2
0x22 read button 3
0x23 read button 4
0x24 read button 5
0x25 read button 6
0x30 reports which buttons have been pushed since last read of this register


read identification

read the identification string of the board.

data sent data recieved explanation
0x95 xx select destination with address 0x94 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
0x94 xx select destination with address 0x94 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
0x94 xx select destination with address 0x94 for WRITE
0x11 xx port 0x11 = set cursor position.
0x25 xx 0x25 = 001 00101 = line 1 position 5.

Default operation

Future hardware enhancements

Future software enhancements



  • Initial public release