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Wiki page [Network] by jim 2013-02-17 20:56:40.
D 2013-02-17T20:56:40.967
L Network
P 0d4d641ddd6111ce7bc16df39aba53c1405003fd
U jim
W 1669
<h1><center>Network Design</center></h1>

The network is half duplex RS-485 network that uses stereo audio cables to connect the nodes. The Web Server computer is connected to the network via USB->Serial adapter and a modified node card.  The network looks like this:

<center><img src="doc/tip/Docs/Images/nodes.png" width="300" height="300"/></center>

The laptop/Web Server is the master on the network and all communication is from master -> node and from node -> master.  In this system there is no need to talk between nodes. The Network Interface (which is a modified Arduino/node) manages the transmit/receive line.  With the RS-485 interfaces you must assert TRANSMIT on the node before you send and drop it to receive data.

<center><img src="doc/tip/Docs/Images/TEK00011.png" /></center>

The top trace shows the TRANSMIT line and the middle shows the master transmitted data, the bottom purple trace shows the received data at a node.

The data packets on the network are ASCII characters/HEX data and the packets look like:

<center><img src="doc/tip/Docs/Images/packet.png" /></center>

There can be up to 32 nodes on the network (RS-485 limitation) and we can run up to 300' of network length.  Address  0 is the broadcast address.  Any packet sent to 0 will be acted on by all the nodes. (Very handy for arming all of them simultaneously).  The nodes have fixed addresses programmed into their EEPROM's and when replying from a broadcast will backoff sending the reply a time based on their address value. (Prevents packet collisions, unfortunately the RS-485 chips don't allow you to do carrier sense like ethernet).

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Z 6c00581010b26c70ccfe0cb7ed2e7b6e