diff --git a/i2c.c b/i2c.c
index 01dc24a..819e9ad 100644
--- a/i2c.c
+++ b/i2c.c
@@ -108,9 +108,23 @@ volatile uint8_t sendbuf[BUFSIZE];
   \param address Address the system should listen to in slave mode, unused
                  when configured for master mode. In master mode, receiver
                  address is given to the send command.
+
+  This also sets the I2C address. In slave mode it's the address we listen on.
+
+  In master mode it's the communication target address. As master one can talk
+  to different devices. Call again i2c_init() for changing the target address,
+  then. Doing so won't interrupt ongoing transmissions and overhead is small.
 */
 void i2c_init(uint8_t address) {
 
+  // In case this is a re-inititalisation,
+  // don't interrupt an ongoing transmission.
+  while (i2c_state & I2C_MODE_BUSY) {
+    delay_us(10);
+  }
+
+  i2c_address = address;
+
   #ifdef I2C_MASTER_MODE
     #ifdef I2C_ENABLE_PULLUPS
       SET_INPUT(SCL);
@@ -135,7 +149,6 @@ void i2c_init(uint8_t address) {
   #endif /* I2C_MASTER_MODE */
 
   #ifdef I2C_SLAVE_MODE
-    i2c_address = address;
     TWAR = i2c_address; // We listen to broadcasts if lowest bit is set.
     TWCR = (0<<TWINT)|(0<<TWEA)|(0<<TWSTA)|(0<<TWSTO)|(1<<TWEN)|(1<<TWIE);
   #endif
@@ -158,12 +171,13 @@ uint8_t i2c_busy(void) {
 /**
   Send a byte to the I2C partner.
 
-  \param address    I2C address of the communications partner.
-
   \param data       The byte to be buffered/sent.
 
   \param last_byte  Wether this is the last byte of a transmission.
 
+  This implementation assumes to talk to mostly one communications client. To
+  set the target, or to change it between transmissions, call i2c_init().
+
   Unlike many other protocols (serial, SPI), I2C has an explicite transmission
   start and transmission end. Invoking code has to tell wether the given byte
   is the last byte of a transmission, so sending code can properly end it.
@@ -187,7 +201,7 @@ uint8_t i2c_busy(void) {
   limitation is, one can end a transmisson by simply not writing for a while,
   until it's sure the buffer became empty.
 */
-void i2c_write(uint8_t address, uint8_t data, uint8_t last_byte) {
+void i2c_write(uint8_t data, uint8_t last_byte) {
 
   while (i2c_should_end || ! buf_canwrite(send)) {
     delay_us(10);
@@ -195,12 +209,7 @@ void i2c_write(uint8_t address, uint8_t data, uint8_t last_byte) {
 
   if (i2c_state & I2C_MODE_FREE) {
     // No transmission ongoing, start one.
-    i2c_address = address;
-
-    // Just send.
     i2c_state = I2C_MODE_SAWP;
-
-    // Start transmission.
     TWCR = (1<<TWINT)|(0<<TWEA)|(1<<TWSTA)|(0<<TWSTO)|(1<<TWEN)|(1<<TWIE);
     i2c_state |= I2C_MODE_BUSY;
   }
diff --git a/i2c.h b/i2c.h
index 35f2827..34de753 100644
--- a/i2c.h
+++ b/i2c.h
@@ -40,7 +40,7 @@
 
 void i2c_init(uint8_t address);
 uint8_t i2c_busy(void);
-void i2c_write(uint8_t address, uint8_t data, uint8_t last_byte);
+void i2c_write(uint8_t data, uint8_t last_byte);
 
 #endif /* I2C */
 
diff --git a/i2c_test.c b/i2c_test.c
index c7ffd4a..ce034ff 100644
--- a/i2c_test.c
+++ b/i2c_test.c
@@ -162,8 +162,7 @@ static void i2c_test(void) {
 
   for (i = 0; i < sizeof(display_init); i++) {
     // Send last byte with 'last_byte' set.
-    i2c_write(DISPLAY_I2C_ADDRESS, pgm_read_byte(&display_init[i]),
-              (i == sizeof(display_init) - 1));
+    i2c_write(pgm_read_byte(&display_init[i]), (i == sizeof(display_init) - 1));
   }
 
   /**
@@ -172,20 +171,20 @@ static void i2c_test(void) {
     zeros, byte by byte.
   */
   // Set horizontal adressing mode.
-  i2c_write(DISPLAY_I2C_ADDRESS, 0x00, 0);
-  i2c_write(DISPLAY_I2C_ADDRESS, 0x20, 0);
-  i2c_write(DISPLAY_I2C_ADDRESS, 0x00, 1);
+  i2c_write(0x00, 0);
+  i2c_write(0x20, 0);
+  i2c_write(0x00, 1);
 
   // Write 512 zeros.
-  i2c_write(DISPLAY_I2C_ADDRESS, 0x40, 0);
+  i2c_write(0x40, 0);
   for (i = 0; i < 512; i++) {
-    i2c_write(DISPLAY_I2C_ADDRESS, 0x00, (i == 511));
+    i2c_write(0x00, (i == 511));
   }
 
   // Return to page adressing mode.
-  i2c_write(DISPLAY_I2C_ADDRESS, 0x00, 0);
-  i2c_write(DISPLAY_I2C_ADDRESS, 0x20, 0);
-  i2c_write(DISPLAY_I2C_ADDRESS, 0x02, 1);
+  i2c_write(0x00, 0);
+  i2c_write(0x20, 0);
+  i2c_write(0x02, 1);
 
   /**
     Setup cursor on display.
@@ -193,32 +192,31 @@ static void i2c_test(void) {
     "Welcome to Teacup" is 64 pixel columns wide, entire display is
     128 columns, so we offset by 32 columns to get it to the center.
   */
-  i2c_write(DISPLAY_I2C_ADDRESS, 0x00, 0);
+  i2c_write(0x00, 0);
   // Line 1.
-  i2c_write(DISPLAY_I2C_ADDRESS, 0xB0 | 1, 0);
+  i2c_write(0xB0 | 1, 0);
   // Column 32.
-  i2c_write(DISPLAY_I2C_ADDRESS, 0x00 | (32 & 0x0F), 0);
-  i2c_write(DISPLAY_I2C_ADDRESS, 0x10 | ((32 >> 4) & 0x0F), 1);
+  i2c_write(0x00 | (32 & 0x0F), 0);
+  i2c_write(0x10 | ((32 >> 4) & 0x0F), 1);
 
   // Render text to bitmap to display.
-  i2c_write(DISPLAY_I2C_ADDRESS, 0x40, 0);
+  i2c_write(0x40, 0);
   while (*message) {
     uint8_t index = (uint8_t)*message - 0x20;
 
     // Send the character bitmap.
     for (i = 0; i < pgm_read_byte(&font_8x4[index].columns); i++) {
-      i2c_write(DISPLAY_I2C_ADDRESS,
-                pgm_read_byte(&font_8x4[index].data[i]), 0);
+      i2c_write(pgm_read_byte(&font_8x4[index].data[i]), 0);
     }
     // Send space between characters.
     for (i = 0; i < FONT_SYMBOLS_SPACE; i++) {
-      i2c_write(DISPLAY_I2C_ADDRESS, 0x00, 0);
+      i2c_write(0x00, 0);
     }
 
     message++;
   }
   // Send another space for transmission end.
-  i2c_write(DISPLAY_I2C_ADDRESS, 0x00, 1);
+  i2c_write(0x00, 1);
 }
 
 #endif /* I2C_TEST */
diff --git a/mendel.c b/mendel.c
index 8f549af..a6280f8 100644
--- a/mendel.c
+++ b/mendel.c
@@ -96,7 +96,7 @@ void init(void) {
   #endif
 
   #ifdef I2C
-    i2c_init(0);
+    i2c_init(DISPLAY_I2C_ADDRESS);
   #endif
 
 	// set up timers