User Interface

The RPi_UI PCB

This is the documentation page for the RPi_UI board.

External resources

Datasheets

• MCP79412 (I2C RTC)
• MCP79522 (SPI RTC)

Pinout

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.

LEDs

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)

Protocol

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

examples

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.

Changelog

1.0

• Initial public release