ARDUINO W5100 WebClient 测试

基础工作：W5100扩展板插在ARDUINO上。用网线把W5100和自己家的路由器连接。插上网线能看到侧面网口指示灯变亮。路由器开启DHCP服务（一般都是开启的）。

1.打开官方例程里面的Ethernet->WebClient

2.修改里面的谷歌服务器为百度的。

3.修改IP地址为本地的局域网号码段，比如你的电脑是192.168.1.100。那么设置你的w5100，也在192.168.1.x。后面的x不能与局域网内的其它设备重复。

4.下载代码，看效果。

 /*
   Web client

  This sketch connects to a website (http://www.google.com)
  using an Arduino Wiznet Ethernet shield. 

  Circuit:
  * Ethernet shield attached to pins 10, 11, 12, 13

  created 18 Dec 2009
  by David A. Mellis
  modified 9 Apr 2012
  by Tom Igoe, based on work by Adrian McEwen

  */

 #include <SPI.h>
 #include <Ethernet.h>

 // Enter a MAC address for your controller below.
 // Newer Ethernet shields have a MAC address printed on a sticker on the shield
 byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
 // if you don't want to use DNS (and reduce your sketch size)
 // use the numeric IP instead of the name for the server:
 //IPAddress server(74,125,232,128);  // numeric IP for Google (no DNS)
 char server[] = "www.baidu.com";    // name address for Google (using DNS)

 // Set the static IP address to use if the DHCP fails to assign
 IPAddress ip(,,,);

 // Initialize the Ethernet client library
 // with the IP address and port of the server
 // that you want to connect to (port 80 is default for HTTP):
 EthernetClient client;

 void setup() {
  // Open serial communications and wait for port to open:
   Serial.begin();
    while (!Serial) {
     ; // wait for serial port to connect. Needed for Leonardo only
   }

   // start the Ethernet connection:
   if (Ethernet.begin(mac) == ) {
     Serial.println("Failed to configure Ethernet using DHCP");
     // no point in carrying on, so do nothing forevermore:
     // try to congifure using IP address instead of DHCP:
     Ethernet.begin(mac, ip);
   }
   // give the Ethernet shield a second to initialize:
   delay();
   Serial.println("connecting...");

   // if you get a connection, report back via serial:
   if (client.connect(server, )) {
     Serial.println("connected");
     // Make a HTTP request:
     client.println("GET /search?q=arduino HTTP/1.1");
     client.println("Host: www.baidu.com");
     client.println("Connection: close");
     client.println();
   }
   else {
     // kf you didn't get a connection to the server:
     Serial.println("connection failed");
   }
 }

 void loop()
 {
   // if there are incoming bytes available
   // from the server, read them and print them:
   if (client.available()) {
     char c = client.read();
     Serial.print(c);
   }

   // if the server's disconnected, stop the client:
   if (!client.connected()) {
     Serial.println();
     Serial.println("disconnecting.");
     client.stop();

     // do nothing forevermore:
     while(true);
   }
 }

能显示服务器返回的数据，证明通讯成功。