Ethernet Shield for Arduino UNO Mega

The Arduino Ethernet Shield allows an Arduino board to connect to the internet.
It is based on the Wiznet W5100 ethernet chip (datasheet).
The Wiznet W5100 provides a network (IP) stack capable of both TCP and UDP.
It supports up to four simultaneous socket connections.
Use the Ethernet library to write sketches which connect to the internet using the shield.
The ethernet shield connects to an Arduino board using long wire-wrap headers which extend through the shield.
This keeps the pin layout intact and allows another shield to be stacked on top.

Features:
Works as a server or client.
Direct plug-board, requires no soldering.
Controller: W5100
Compatible with Arduino motherboard, 2009, United Nations, 1280 mega, mega 2560 etc.
The shield provides a standard RJ45 ethernet jack.
The latest revision of the shield adds a micro-SD card slot
The reset button on the shield resets both the W5100 and the Arduino board.
The shield contains a number of informational LEDs:
PWR: indicates that the board and shield are powered
LINK: indicates the presence of a network link and flashes when the shield transmits or receives data
FULLD: indicates that the network connection is full duplex
100M: indicates the presence of a 100 Mb/s network connection (as opposed to 10 Mb/s)
RX: flashes when the shield receives data
TX: flashes when the shield sends data
COLL: flashes when network collisions are detected