Additional details for I2C_SLAVE_ADDRESS

.travis.yml

   #
   - restore_configs
   - opt_enable_adv BEZIER_CURVE_SUPPORT EXPERIMENTAL_I2CBUS
-  - opt_set_adv I2C_SLAVE_ADDRESS 1
+  - opt_set_adv I2C_SLAVE_ADDRESS 63
   - build_marlin
   #
   # Enable COREXY

Marlin/Configuration_adv.h

 // @section i2cbus
 
 //#define EXPERIMENTAL_I2CBUS
-#define I2C_SLAVE_ADDRESS  0 // Set non-zero to act as a slave
+#define I2C_SLAVE_ADDRESS  0 // Set a value from 8 to 127 to act as a slave
 
 #endif // CONFIGURATION_ADV_H

Marlin/Marlin_main.cpp

     }
   }
 
-#endif //EXPERIMENTAL_I2CBUS
+#endif // EXPERIMENTAL_I2CBUS
 
 /**
  * M200: Set filament diameter and set E axis units to cubic units

Marlin/SanityCheck.h

 #if ENABLED(EMERGENCY_PARSER) && defined(USBCON)
   #error "EMERGENCY_PARSER does not work on boards with AT90USB processors (USBCON)."
 #endif
+
+/**
+ * I2C bus
+ */
+#if ENABLED(EXPERIMENTAL_I2CBUS) && I2C_SLAVE_ADDRESS > 0
+  #if I2C_SLAVE_ADDRESS < 8
+    #error "I2C_SLAVE_ADDRESS can't be less than 8. (Addresses 0 - 7 are reserved.)"
+  #elif I2C_SLAVE_ADDRESS > 127
+    #error "I2C_SLAVE_ADDRESS can't be over 127. (Only 7 bits allowed.)"
+  #endif
+#endif

Marlin/example_configurations/Cartesio/Configuration_adv.h

 // @section i2cbus
 
 //#define EXPERIMENTAL_I2CBUS
-#define I2C_SLAVE_ADDRESS  0 // Set non-zero to act as a slave
+#define I2C_SLAVE_ADDRESS  0 // Set a value from 8 to 127 to act as a slave
 
 #endif // CONFIGURATION_ADV_H

Marlin/example_configurations/Felix/Configuration_adv.h

 // @section i2cbus
 
 //#define EXPERIMENTAL_I2CBUS
-#define I2C_SLAVE_ADDRESS  0 // Set non-zero to act as a slave
+#define I2C_SLAVE_ADDRESS  0 // Set a value from 8 to 127 to act as a slave
 
 #endif // CONFIGURATION_ADV_H

Marlin/example_configurations/Hephestos/Configuration_adv.h

 // @section i2cbus
 
 //#define EXPERIMENTAL_I2CBUS
-#define I2C_SLAVE_ADDRESS  0 // Set non-zero to act as a slave
+#define I2C_SLAVE_ADDRESS  0 // Set a value from 8 to 127 to act as a slave
 
 #endif // CONFIGURATION_ADV_H

Marlin/example_configurations/Hephestos_2/Configuration_adv.h

 // @section i2cbus
 
 //#define EXPERIMENTAL_I2CBUS
-#define I2C_SLAVE_ADDRESS  0 // Set non-zero to act as a slave
+#define I2C_SLAVE_ADDRESS  0 // Set a value from 8 to 127 to act as a slave
 
 #endif // CONFIGURATION_ADV_H

Marlin/example_configurations/K8200/Configuration_adv.h

 // @section i2cbus
 
 //#define EXPERIMENTAL_I2CBUS
-#define I2C_SLAVE_ADDRESS  0 // Set non-zero to act as a slave
+#define I2C_SLAVE_ADDRESS  0 // Set a value from 8 to 127 to act as a slave
 
 #endif // CONFIGURATION_ADV_H

Marlin/example_configurations/K8400/Configuration_adv.h

 // @section i2cbus
 
 //#define EXPERIMENTAL_I2CBUS
-#define I2C_SLAVE_ADDRESS  0 // Set non-zero to act as a slave
+#define I2C_SLAVE_ADDRESS  0 // Set a value from 8 to 127 to act as a slave
 
 #endif // CONFIGURATION_ADV_H

Marlin/example_configurations/RigidBot/Configuration_adv.h

 // @section i2cbus
 
 //#define EXPERIMENTAL_I2CBUS
-#define I2C_SLAVE_ADDRESS  0 // Set non-zero to act as a slave
+#define I2C_SLAVE_ADDRESS  0 // Set a value from 8 to 127 to act as a slave
 
 #endif // CONFIGURATION_ADV_H

Marlin/example_configurations/SCARA/Configuration_adv.h

 // @section i2cbus
 
 //#define EXPERIMENTAL_I2CBUS
-#define I2C_SLAVE_ADDRESS  0 // Set non-zero to act as a slave
+#define I2C_SLAVE_ADDRESS  0 // Set a value from 8 to 127 to act as a slave
 
 #endif // CONFIGURATION_ADV_H

Marlin/example_configurations/TAZ4/Configuration_adv.h

 // @section i2cbus
 
 //#define EXPERIMENTAL_I2CBUS
-#define I2C_SLAVE_ADDRESS  0 // Set non-zero to act as a slave
+#define I2C_SLAVE_ADDRESS  0 // Set a value from 8 to 127 to act as a slave
 
 #endif // CONFIGURATION_ADV_H

Marlin/example_configurations/WITBOX/Configuration_adv.h

 // @section i2cbus
 
 //#define EXPERIMENTAL_I2CBUS
-#define I2C_SLAVE_ADDRESS  0 // Set non-zero to act as a slave
+#define I2C_SLAVE_ADDRESS  0 // Set a value from 8 to 127 to act as a slave
 
 #endif // CONFIGURATION_ADV_H

Marlin/example_configurations/delta/biv2.5/Configuration_adv.h

 // @section i2cbus
 
 //#define EXPERIMENTAL_I2CBUS
-#define I2C_SLAVE_ADDRESS  0 // Set non-zero to act as a slave
+#define I2C_SLAVE_ADDRESS  0 // Set a value from 8 to 127 to act as a slave
 
 #endif // CONFIGURATION_ADV_H

Marlin/example_configurations/delta/generic/Configuration_adv.h

 // @section i2cbus
 
 //#define EXPERIMENTAL_I2CBUS
-#define I2C_SLAVE_ADDRESS  0 // Set non-zero to act as a slave
+#define I2C_SLAVE_ADDRESS  0 // Set a value from 8 to 127 to act as a slave
 
 #endif // CONFIGURATION_ADV_H

Marlin/example_configurations/delta/kossel_mini/Configuration_adv.h

 // @section i2cbus
 
 //#define EXPERIMENTAL_I2CBUS
-#define I2C_SLAVE_ADDRESS  0 // Set non-zero to act as a slave
+#define I2C_SLAVE_ADDRESS  0 // Set a value from 8 to 127 to act as a slave
 
 #endif // CONFIGURATION_ADV_H

Marlin/example_configurations/delta/kossel_pro/Configuration_adv.h

 // @section i2cbus
 
 //#define EXPERIMENTAL_I2CBUS
-#define I2C_SLAVE_ADDRESS  0 // Set non-zero to act as a slave
+#define I2C_SLAVE_ADDRESS  0 // Set a value from 8 to 127 to act as a slave
 
 #endif // CONFIGURATION_ADV_H

Marlin/example_configurations/delta/kossel_xl/Configuration_adv.h

 // @section i2cbus
 
 //#define EXPERIMENTAL_I2CBUS
-#define I2C_SLAVE_ADDRESS  0 // Set non-zero to act as a slave
+#define I2C_SLAVE_ADDRESS  0 // Set a value from 8 to 127 to act as a slave
 
 #endif // CONFIGURATION_ADV_H

Marlin/example_configurations/makibox/Configuration_adv.h

 // @section i2cbus
 
 //#define EXPERIMENTAL_I2CBUS
-#define I2C_SLAVE_ADDRESS  0 // Set non-zero to act as a slave
+#define I2C_SLAVE_ADDRESS  0 // Set a value from 8 to 127 to act as a slave
 
 #endif // CONFIGURATION_ADV_H

Marlin/example_configurations/tvrrug/Round2/Configuration_adv.h

 // @section i2cbus
 
 //#define EXPERIMENTAL_I2CBUS
-#define I2C_SLAVE_ADDRESS  0 // Set non-zero to act as a slave
+#define I2C_SLAVE_ADDRESS  0 // Set a value from 8 to 127 to act as a slave
 
 #endif // CONFIGURATION_ADV_H

Marlin/twibus.cpp

 }
 
 void TWIBus::address(const uint8_t adr) {
+  if (adr < 8 || adr > 127) {
+    SERIAL_ECHO_START;
+    SERIAL_ECHOLNPGM("Bad I2C address (8-127)");
+  }
+
   this->addr = adr;
 
   #if ENABLED(DEBUG_TWIBUS)