10LOL display board (10mm rgb led charlieplexed display matrix)
====

Hardware designs and firmware for a modular matrix display board.

Each module consists of an LED carrier board and a driver board.

Supply voltage is 7-20V (with onboard switching regulator).
TODO: Figure out actual power requirements, and if a single regulator can power
multiple modules.

The control board 
Modules operate autonomously,  module operates autonomously, accepting data over SPI.
The modules can be programmed with unique addresses, allowing
multiple modules on a single SPI bus.


SPI communication protocol
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Commands are 4 bytes.  The first byte identidies the command, followed by 3
bytes of argument data (d0-d2).

On power-up the board will be in disconnected state.  A disconnect command
followed by a connect command should be used to ensure the serial interface
is coherent, and the board is in the ready state.

Command 0xe1 puts the specified board into the active state (other
previously active boards return to the ready state).

Commands <0xd0 are ignored when the board is not active.

Commands are as follows:

0x00 - 0x3f: Write pixel
 Pixels numbered left-right,then top-bottom)
  d0: red
  d1: green
  d2: blue

0x80: Page flip
 Set the framebuffer page for both display and pixel writing.
 This allows double buffered updates
  d0: Unused(0)
  d1: display page number
  d2: pixel write page number

0xa0: Initialize FORTH
 Initialize and enable the FORTH interpreter.
 The forth dictionary is stored at the end of the framebuffer.
  d0: rstack size (cells)
  d1: Dictionary size (in 256-byte framebuffer pages)
  d2: Unused (0)

0xa1: FORTH source
 Send one to three bytes of FORTH source code.  Null (0) characters are ignored.
  d0: First character
  d1: Second character
  d2: Third character

0xc0: Set brightness
 Sets brightness/color ballance (stored in EEPROM)
  d0: Red brightness
  d1: Green brightness
  d2: Blue brightness

0xd0: Set board address
 Modifies the board address (stored in EEPROM).
 The board will only respond to this address if the SDA pin is pulled low.
 This allows the addresses to be set without disconnecting the board.
  d0: 0xf5
  d1: 0xf0 + high address nibble
  d2: 0xf0 + low address nibble

0xe0: Connect
 Prepares the board for other commands
  d0: 0xf0
  d1: 0xf1
  d2: 0xf2

0xe1: Board select
 Only the selected board will respond to most commands.
  d0: board address (0xff to select all boards)
  d1: Unused (0)
  d2: Unused (0)

0xff: Disconnect
 Reset serial interface.
 The connect command must be sent before any other commands.
 The data bytes on this command are optional.  However sending the full
 sequence bytes ensures that the board is preoperly aligned with the
 four byte command boundary.
  d0: 0xff
  d1: 0xff
  d2: 0xff