4 files changed, 81 insertions, 5 deletions
diff --git a/libraries/Wire/examples/digital_potentiometer/digital_potentiometer.ino b/libraries/Wire/examples/digital_potentiometer/digital_potentiometer.ino
index 5fb91fb..dd40a25 100644
--- a/libraries/Wire/examples/digital_potentiometer/digital_potentiometer.ino
+++ b/libraries/Wire/examples/digital_potentiometer/digital_potentiometer.ino
@@ -9,8 +9,6 @@
 
 // This example code is in the public domain.
 
-// This example code is in the public domain.
-
 
 #include <Wire.h>
 
diff --git a/libraries/Wire/examples/i2c_scanner/i2c_scanner.ino b/libraries/Wire/examples/i2c_scanner/i2c_scanner.ino
new file mode 100644
index 0000000..3febbf4
--- /dev/null
+++ b/libraries/Wire/examples/i2c_scanner/i2c_scanner.ino
@@ -0,0 +1,75 @@
+// --------------------------------------
+// i2c_scanner
+//
+// Version 1
+//    This program (or code that looks like it)
+//    can be found in many places.
+//    For example on the Arduino.cc forum.
+//    The original author is not know.
+// Version 2, Juni 2012, Using Arduino 1.0.1
+//     Adapted to be as simple as possible by Arduino.cc user Krodal
+// Version 3, Feb 26  2013
+//    V3 by louarnold
+// Version 4, March 3, 2013, Using Arduino 1.0.3
+//    by Arduino.cc user Krodal.
+//    Changes by louarnold removed.
+//    Scanning addresses changed from 0...127 to 1...119,
+//    according to the i2c scanner by Nick Gammon
+//    https://www.gammon.com.au/forum/?id=10896
+// Version 5, March 28, 2013
+//    As version 4, but address scans now to 127.
+//    A sensor seems to use address 120.
+// Version 6, November 27, 2015.
+//    Added waiting for the Leonardo serial communication.
+//
+//
+// This sketch tests the standard 7-bit addresses
+// Devices with higher bit address might not be seen properly.
+//
+
+#include <Wire.h>
+
+void setup() {
+  Wire.begin();
+
+  Serial.begin(9600);
+  while (!Serial); // Leonardo: wait for serial monitor
+  Serial.println("\nI2C Scanner");
+}
+
+void loop() {
+  int nDevices = 0;
+
+  Serial.println("Scanning...");
+
+  for (byte address = 1; address < 127; ++address) {
+    // The i2c_scanner uses the return value of
+    // the Write.endTransmisstion to see if
+    // a device did acknowledge to the address.
+    Wire.beginTransmission(address);
+    byte error = Wire.endTransmission();
+
+    if (error == 0) {
+      Serial.print("I2C device found at address 0x");
+      if (address < 16) {
+        Serial.print("0");
+      }
+      Serial.print(address, HEX);
+      Serial.println("  !");
+
+      ++nDevices;
+    } else if (error == 4) {
+      Serial.print("Unknown error at address 0x");
+      if (address < 16) {
+        Serial.print("0");
+      }
+      Serial.println(address, HEX);
+    }
+  }
+  if (nDevices == 0) {
+    Serial.println("No I2C devices found\n");
+  } else {
+    Serial.println("done\n");
+  }
+  delay(5000); // Wait 5 seconds for next scan
+}
diff --git a/libraries/Wire/src/Wire.cpp b/libraries/Wire/src/Wire.cpp
index d2146f7..58916ce 100644
--- a/libraries/Wire/src/Wire.cpp
+++ b/libraries/Wire/src/Wire.cpp
@@ -17,6 +17,7 @@
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  
   Modified 2012 by Todd Krein (todd@krein.org) to implement repeated starts
+  Modified 2017 by Chuck Todd (ctodd@cableone.net) to correct Unconfigured Slave Mode reboot
 */
 
 extern "C" {
@@ -60,14 +61,14 @@ void TwoWire::begin(void)
   txBufferLength = 0;
 
   twi_init();
+  twi_attachSlaveTxEvent(onRequestService); // default callback must exist
+  twi_attachSlaveRxEvent(onReceiveService); // default callback must exist
 }
 
 void TwoWire::begin(uint8_t address)
 {
-  twi_setAddress(address);
-  twi_attachSlaveTxEvent(onRequestService);
-  twi_attachSlaveRxEvent(onReceiveService);
   begin();
+  twi_setAddress(address);
 }
 
 void TwoWire::begin(int address)
diff --git a/libraries/Wire/src/utility/twi.c b/libraries/Wire/src/utility/twi.c
index 171af73..1a35146 100644
--- a/libraries/Wire/src/utility/twi.c
+++ b/libraries/Wire/src/utility/twi.c
@@ -445,6 +445,7 @@ ISR(TWI_vect)
     case TW_MR_DATA_ACK: // data received, ack sent
       // put byte into buffer
       twi_masterBuffer[twi_masterBufferIndex++] = TWDR;
+      __attribute__ ((fallthrough));
     case TW_MR_SLA_ACK:  // address sent, ack received
       // ack if more bytes are expected, otherwise nack
       if(twi_masterBufferIndex < twi_masterBufferLength){
@@ -530,6 +531,7 @@ ISR(TWI_vect)
         twi_txBufferLength = 1;
         twi_txBuffer[0] = 0x00;
       }
+      __attribute__ ((fallthrough));		  
       // transmit first byte from buffer, fall
     case TW_ST_DATA_ACK: // byte sent, ack returned
       // copy data to output register