Arduino Ethernet UDPSendReceive example disables all pin outputs? - udp

Question

The UDPSendReceive.pde example bundled with the IDE works fine out of the box and displays the correct output on the serial monitor when it receives UDP packets, but seems to disable all the pinOutputs?
#include <SPI.h> // needed for Arduino versions later than 0018
#include <Ethernet.h>
#include <EthernetUdp.h> // UDP library from: bjoern#cs.stanford.edu 12/30/2008
// Enter a MAC address and IP address for your controller below.
// The IP address will be dependent on your local network:
byte mac[] = {
0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
IPAddress ip(192, 168, 1, 177);
unsigned int localPort = 8888; // local port to listen on
// buffers for receiving and sending data
char packetBuffer[UDP_TX_PACKET_MAX_SIZE]; //buffer to hold incoming packet,
char ReplyBuffer[] = "acknowledged"; // a string to send back
// An EthernetUDP instance to let us send and receive packets over UDP
EthernetUDP Udp;
void setup() {
// start the Ethernet and UDP:
Ethernet.begin(mac,ip);
Udp.begin(localPort);
Serial.begin(9600);
pinMode(12, OUTPUT);
}
void loop() {
// if there's data available, read a packet
int packetSize = Udp.parsePacket();
if(packetSize)
{
Serial.print("Received packet of size ");
Serial.println(packetSize);
Serial.print("From ");
IPAddress remote = Udp.remoteIP();
for (int i =0; i < 4; i++)
{
Serial.print(remote[i], DEC);
if (i < 3)
{
Serial.print(".");
}
}
Serial.print(", port ");
Serial.println(Udp.remotePort());
// read the packet into packetBufffer
Udp.read(packetBuffer,UDP_TX_PACKET_MAX_SIZE);
Serial.println("Contents:");
Serial.println(packetBuffer);
// send a reply, to the IP address and port that sent us the packet we received
Udp.beginPacket(Udp.remoteIP(), Udp.remotePort());
Udp.write(ReplyBuffer);
Udp.endPacket();
digitalWrite(12, HIGH); // set the LED on
}
delay(10);
}
Even just changing the loop to be
void loop() {
// if there's data available, read a packet
int packetSize = Udp.parsePacket();
if(packetSize)
{
digitalWrite(12, HIGH);
}
means nothing happens on my outputs (in this case an LED)

Answer 1

Update - Just noticed the SPI include in your code.The SPI library uses pin 12 (for MOSI) so its already reserved.
Previous:
Not sure which Ethernet shield/board you are using, but typically they use SPI protocol to communicate over pins 10-13. Pin 12 is used for MISO. (That's Master In, Slave Out - so its used by the Ethernet device (Slave) as output to the Aurduino's in (Master).
So pins 1 thru 9 should be fine to use as an LED indicator.

Answer 2

The information provided by JDH is correct. Ethernet/SPI uses several pins to communicate with the Ethernet shield. The rest are free for your use. See http://arduino.cc/en/Reference/SPI for some details. The Connections section shows what pins are used by several common Arduino boards. For the Uno and Duemilanove it's pins 10-13.