This is a protocol to interface RS232 to an A16 D32 bus SLOWLY!
It has extra 'commands' added to ease address decoding in some circumstances.

Serial Port Settings:
o 115200 BAUD, no parity, 1 stop bit, no flow control.

Protocol:
o Data arranged in 8 byte messages.
o A message sent always generates a message reply. 
o To overcome message failures a timeout will reset the serial receiver
  if it does not recieve all bytes in "long" time. The software
  should do the same.
o Keep in mind a message sent could be used to reset a module and hence no
  reply message will be recieved.


MESSAGE FORMAT:
===============

TX_MSG = TARGET,
         COMMAND,
         ADDR(7:0),
         ADDR(15:8),
         DATA(7:0),
         DATA(15:8),
         DATA(23:16),
         DATA(31:24) 
		 	
RX_MSG = same as TX_MSG, except with new data (if generated) and 
         COMMAND LSbit = 1


MESSAGE COMPONENT DESCRIPTIONS:
===============================

TARGET:
-------

0x00-0x07 = FE module 0-7
0x08      = BE module
0x09      = BE-Trigger module
0x10      = Development board
0x11      = DevBoard 2 (for testing with more than one target)

TARGET selects which module acts on the serial bit stream. No routing is
done - the data goes to every module. Each module has a hardwired
number (TARGET ID) which dictates which messages it should reply to.

Unused destinations will be ignored. If 2 modules reply to the same
request, we will have garbled data, and a problem!


COMMAND:
-------- 
                        Reply  (DATA):
0x00 = Test	            0x01   (0xA110A110)              
0x02 = Write            0x03   (write data)
0x04 = Read             0x05   (read data)
0x06 = Read_ROM         0x07   (Read-Only-Memory data read)
0x08 = Read_FIFO        0x09   (FIFO Read)
0x0A = Read_FIFO_Stat   0x0B   (FIFO depth counter + full/empty flags)
0x0C = Status           0x0D   (non-memory mapped flags/data)
0x0E = Reset            0x0F   (undefined)
0x10 = Send Trigger     0x11   (0xEEEEAAAA)

0x40 = User Write 0     0x81   (undefined)
0x42 = User Write 1     0x83   (undefined)
0x44 = User Write 2     0x85   (undefined)
0x46 = User Write 3     0x87   (undefined)
0x48 = User Write 4     0x89   (undefined)
0x4a = User Write 5     0x8b   (undefined)
0x4c = User Write 6     0x8d   (undefined)
0x4e = User Write 7     0x8f   (undefined)

0x80 = User Read 0      0x81   (undefined)
0x82 = User Read 1      0x83   (undefined)
0x84 = User Read 2      0x85   (undefined)
0x86 = User Read 3      0x87   (undefined)
0x88 = User Read 4      0x89   (undefined)
0x8a = User Read 5      0x8b   (undefined)
0x8c = User Read 6      0x8d   (undefined)
0x8e = User Read 7      0x8f   (undefined)


0xYY = All others       0xYY+1 (0xDEADD0D0)
	


ADDRESS:
--------
Address of the data - maximum 64kBytes
ADDR(1:0) is ignored and assumed 00 (due to 4 byte data width) 


DATA:
-----
Always 4 bytes.



Examples:
---------

For TX=0x0000111104030201 (Test, module = 0)
    RX=0x0001111110All0Al     

For TX=0x0002000178563412 (Write, addr=0x100, data=0x12345678)
    RX=0x0003000178563412     

For TX=0x0004000100000000 (Read - addr=0x100, data=0x12345678)
	 RX=0x0005000178563412