A simple to use yet powerful system for communicating using RS232, RS485, etc between Arduinos, chipKITs, PCs, etc.

All values are 8-bit and symbolic names are ASCII standard values.

Preamble:

 76543210
+--------+
| SOH    |
+--------+
| SOH    |
+--------+
| SOH    |
+--------+
| SOH    |
+--------+

Packet:

 76543210
+--------+
| SOH    |
+--------+
| DestID |
+--------+
| OrigID |
+--------+
| Cmd    |
+--------+
| DatLen |
+--------+
| STX    |
+--------+
| Data 0 |
| Data 1 |
| ...    |
| Data N |
+--------+
| ETX    |
+--------+
| Cksum  |
+--------+
| EOT    |
+--------+

Checksum is sum of all bytes between (but not including) SOH and ETX, modulus 256.

Special destination address 0x00 is the broadcast. All stations will receive and act upon messages sent to this address.

Addresses that equate to the ASCII symbols SOH etc should be avoided.

Packet reception and identification is through a 6-byte sliding window identifying the header of a packet. As bytes arrive they enter the top of the window and they work their way down to the bottom as more bytes arrive. When the first byte of the window is SOH, the last byte is STX, and the Dest ID is either 0x00 or the ID of the receiving station, it is assumed a valid packet is arriving. From this point on DatLen bytes are then read into the data buffer. If the next three bytes do not equal ETX, the valid checksum, and EOT, then the packet is rejected. Otherwise the function associated with Command is executed.

See example file RemoteLEDReciever and RemoteLEDSender for small change that makes this work with ChainDuinos http://largewire.com/