lpc_spi_hub

SPI hub for alpha-numeric display and keyboard based on LPC11U24 MCU

Board Capabilities

1. Update the display:

• as the whole
• by line
• by row/column/length

2. Control backlight value
3. Set the state of two status LEDs
4. Check for button presses

SPI protocol specification

Packet format

Byte offset	0	1	2	3
Meaning	Preamble 0xAA	Data Len (Cmd.code + Data)	Cmd.code + Op.code	Data

Every packet must be started with a preamble.

Data length is provided in bytes and can't be longer than 127 bytes.

Command code is a higher nibble of the byte (bits 7..4).

Operation code is a lower nibble of the byte (bits 3..0).

List of command codes

Cmd.code	Meaning	Op.codes	Data
0b0000	Update the display	See below	Text string
0b0001	Set backlight value	Backlight value (1..15)	No
0b0010	Set state of status LEDs	No	1 byte (See below)

List of operation codes for "Update the display" command

Op.code	Meaning
0b0000	Clear display
0b0001	Write to whole display
0b0002	Write line
0b0002	Write at row/column

First data byte contents row and column number for addressing the LCD output.

Bit no.	7	6..5	4..0
Meaning	Reserved	Row index (0..3)	Column index (0..19)

Packet example for "Update the display" command

Byte offset	0	1	2	3	4	5	6	7
Value	0xAA	0x06 (5 bytes + Cmd.code)	0x02 Write line	0x00 Line 0	0x54 ('T')	0x65 ('e')	0x73 ('s')	0x74 ('t')

Data byte for "Set state of status LEDs" command

State of up to 7 LEDs can be set

Bit offset (MSB first)	7	6	5	4	3	2	1	0
Meaning	Reserved	LED6	LED5	LED4	LED3	LED2	LED1	LED0

0 means switch LED off, 1 - switch LED on.

Reading state of the buttons

Every byte transmitted from an SPI master will be responsed with a state of the buttons through MISO line.

Bit offset (MSB first)	7	6	5	4	3	2	1	0
Meaning	BTN7	BTN6	BTN5	BTN4	BTN3	BTN2	BTN1	BTN0

0 means switch button was not pressed, 1 - button was pressed.

All bits will be reser after readout.