Added functionality from http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1192228140 which gives the ability to check if an address is in use.

Method added: Wire.checkAddress(address)

Author: lstoll

Wire/Wire.cpp

@@ -256,6 +256,16 @@ void TwoWire::onRequest( void (*function)(void) )
  user_onRequest = function;
 }
 
+// used to check an address - from/see from http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1192228140/2#2
+// modded by lstoll@lstoll.net (wasn't returning result)
+bool TwoWire::checkAddress(uint8_t twiAddress)
+{
+uint8_t *txBuffer;
+twi_writeTo(twiAddress, txBuffer, 0, 1);
+return twi_isFound();
+}
+
+
 // Preinstantiate Objects //////////////////////////////////////////////////////
 
 TwoWire Wire = TwoWire();

Wire/Wire.h

@@ -59,9 +59,13 @@ class TwoWire
  uint8_t receive(void);
  void onReceive( void (*)(int) );
  void onRequest( void (*)(void) );
+// function to check address - from http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1192228140/2#2
+bool checkAddress(uint8_t);
 };
 
 extern TwoWire Wire;
 
+#define WIRE_LIB_SCAN_MOD // notes the check address function has been added. ref http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1192228140/3#3
+
 #endif
 

Wire/utility/twi.c

@@ -310,6 +310,25 @@ void twi_releaseBus(void)
  twi_state = TWI_READY;
 }
 
+/* 
+ * Function twi_isFound
+ * Desc method to see if a device was found after writing to an adddress
+ * Input none
+ * Output true(1) if a device was found, false(0) if not
+ * From: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1192228140/1#1
+ */
+int foundDevice = 0;
+int twi_isFound(void)
+{
+ if (foundDevice)
+ {
+ foundDevice = 0;
+ return 1;
+ }
+
+ return 0;
+}
+
 SIGNAL(SIG_2WIRE_SERIAL)
 {
  switch(TW_STATUS){
@@ -323,6 +342,11 @@ SIGNAL(SIG_2WIRE_SERIAL)
 
  // Master Transmitter
  case TW_MT_SLA_ACK: // slave receiver acked address
+// set found device to true if a device acknowledged the message
+// from http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1192228140/1#1
+ {
+ foundDevice = 1;
+ }
  case TW_MT_DATA_ACK: // slave receiver acked data
  // if there is data to send, send it, otherwise stop 
  if(twi_masterBufferIndex < twi_masterBufferLength){

Wire/utility/twi.h

@@ -17,18 +17,18 @@
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
 */
 
-#ifndef twi_h
-#define twi_h
+#ifndef twi_h
+#define twi_h
 
  #include <inttypes.h>
 
  //#define ATMEGA8
 
- #ifndef CPU_FREQ
+ #ifndef CPU_FREQ
  #define CPU_FREQ 16000000L
  #endif
 
- #ifndef TWI_FREQ
+ #ifndef TWI_FREQ
  #define TWI_FREQ 100000L
  #endif
 
@@ -51,7 +51,9 @@
  void twi_attachSlaveTxEvent( void (*)(void) );
  void twi_reply(uint8_t);
  void twi_stop(void);
- void twi_releaseBus(void);
-
+ void twi_releaseBus(void);
+ // dec for is found method from http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1192228140/1#1
+ int twi_isFound(void);
+
 #endif