Arduino Ethernet Shield R737
The Arduino ethernet shield network enable your Arduino board with a RJ45 ethernet jack. The ethernet shield allows for the convenient placement of the Arduino on your network to report information and receive command via TCP/IP.
Using the Arduino Ethernet Shield
To use the shield, mount it on top of an Arduino board (e.g. the Uno). To upload sketches to the
board, connect it to your computer with a USB cable as you normally would. Once the sketch has been uploaded, you can disconnect the board from your computer and power it with an external power supply.
Connect the shield to your computer or a network hub or router using a standard ethernet cable (CAT5 or CAT6 with RJ45 connectors). Connecting to a computer may require the use of a cross-over cable (although many computers, including all recent Macs can do the cross-over internally).
Assign your Arduino a MAC/IP Address with the Arduino Ethernet Shield
The shield must be assigned a MAC address and a fixed IP address using the Ethernet.begin() function. A MAC address is a globally unique identifier for a particular device. Current Ethernet shields come with a sticker indicating the MAC address you should use with them.
For older shields without a dedicated MAC address, inventing a random one should work, but don't use the same one for multiple boards. Valid IP addresses depend on the configuration of your network. It is possible to use DHCP to dynamically assign an IP to the shield. Optionally, you can also specify a network gateway and subnet.