diff --git a/firmware/Include/main.h b/firmware/Include/main.h
index 6bdfffb..4caf737 100644
--- a/firmware/Include/main.h
+++ b/firmware/Include/main.h
@@ -55,7 +55,10 @@ void Error_Handler(void);
 
 void set_input(uint8_t channel);
 void set_attenuation(uint8_t left, uint8_t right);
-void set_mute(uint8_t mute);
+void set_mute(uint8_t mute); //< tries to switch to muted ui state
+int is_muted(); //< returns whether the ui is muted
+void set_short(uint8_t shorted); //< tries to switch to shorted ui state
+int is_shorted();
 
 /* USER CODE BEGIN EFP */
 
diff --git a/firmware/Src/main.c b/firmware/Src/main.c
index d56aab1..2e9cf68 100644
--- a/firmware/Src/main.c
+++ b/firmware/Src/main.c
@@ -104,51 +104,89 @@ int test_button_pressed() {
 
 struct ui_state {
   uint8_t oldchannel;
-  uint8_t mute;
+  enum {
+    UI_STATE_NORMAL = 0, 
+    UI_STATE_MUTE,
+    UI_STATE_SHORT,
+  } state;
+
 } ui_state = {
   .oldchannel = -1,
-  .mute = 0,
+  .state = UI_STATE_NORMAL,
 };
 
 void set_input(uint8_t channel) {
-	if (ui_state.oldchannel == channel || channel >= 6)
+	if (ui_state.state != UI_STATE_NORMAL || ui_state.oldchannel == channel || channel >= 6)
 		return;
 
-	set_input_led(ui_state.oldchannel, 0);
+  set_input_led(ui_state.oldchannel, 0);	
+  
+  set_input_led(channel, 1);
 
-  // do not disturb the mute mode
-  if (!ui_state.mute)
-  {
-	  set_input_led(channel, 1);
-
-	  // invert bd inputs to match the numbers on the case
-    bd_set_input(&hi2c1, 5-channel);
-  }
+  // invert bd inputs to match the numbers on the case
+  bd_set_input(&hi2c1, 5-channel);
 
 	ui_state.oldchannel = channel;
 
 	printf("C%d\n", channel);
 }
 
+// only mute if the ui allows to 
 void set_mute(uint8_t mute) {
-  if(ui_state.mute == mute)
+  if(UI_STATE_MUTE == ui_state.state && mute)
+    // no state change required
     return;
 
-  if (0 == (ui_state.mute = mute)) {
+  // figure out the state transition  
+  if (UI_STATE_NORMAL == ui_state.state && mute) {
+    ui_state.state = UI_STATE_MUTE;
+    HAL_GPIO_WritePin(USER_LED_GPIO_Port, USER_LED_Pin, 1);
+    set_input_led(ui_state.oldchannel, 0);
+    bd_set_input(&hi2c1, BD_INPUT_MUTE);
+  } 
+  else if (UI_STATE_MUTE == ui_state.state && !mute) 
+  {
+    ui_state.state = UI_STATE_NORMAL;
     // hack to make reactivation of the last channel easier
     uint8_t old_input = ui_state.oldchannel;
     ui_state.oldchannel = -1;
 
     set_input(old_input);
-    HAL_GPIO_WritePin(USER_LED_GPIO_Port, USER_LED_Pin, 0);
-  }
-  else {
-    HAL_GPIO_WritePin(USER_LED_GPIO_Port, USER_LED_Pin, 1);
-    set_input_led(ui_state.oldchannel, 0);
-    bd_set_input(&hi2c1, BD_INPUT_MUTE);
+    HAL_GPIO_WritePin(USER_LED_GPIO_Port, USER_LED_Pin, 0); 
   }
+}
 
-  printf("M%d\n", ui_state.mute?1:0);
+int is_muted() {
+  return ui_state.state == UI_STATE_MUTE;
+}
+
+void set_short(uint8_t do_short) {
+  // test for possible state changes
+  if (UI_STATE_NORMAL == ui_state.state && do_short) 
+  {
+    ui_state.state = UI_STATE_SHORT;
+    bd_set_input(&hi2c1, BD_INPUT_ALL);
+
+    // visualize that all inputs are shorted
+    for (int i = 0; i < 6; ++i) 
+      set_input_led(i, 1);
+  } 
+  else if (UI_STATE_SHORT == ui_state.state && !do_short) 
+  {
+    ui_state.state = UI_STATE_NORMAL;
+    
+    for (int i = 0; i < 6; ++i) 
+      set_input_led(i, 0);
+
+    // reactivate currently selected input
+    uint8_t old_input = ui_state.oldchannel;
+    ui_state.oldchannel = -1;
+    set_input(old_input);
+  }
+}
+
+int is_shorted() {
+  return ui_state.state == UI_STATE_SHORT;
 }
 
 void set_attenuation(uint8_t left, uint8_t right) {
@@ -202,6 +240,7 @@ int main(void)
   set_attenuation(0,0);
   int count = 0;
   int button_timeout = 0;
+  
   /* USER CODE END 2 */
 
   /* Infinite loop */
@@ -226,7 +265,8 @@ int main(void)
 
       if (1000 < button_timeout) {
         // long press, toggle mute
-        set_mute(!ui_state.mute);
+        set_mute(!is_muted());
+        printf("M%d\n", is_muted());
         button_timeout = 0;
       }
 
diff --git a/firmware/Src/message_parser.c b/firmware/Src/message_parser.c
index 695565d..85a11eb 100644
--- a/firmware/Src/message_parser.c
+++ b/firmware/Src/message_parser.c
@@ -156,6 +156,16 @@ int parse_buffer() {
 		if (next_arg_unsigned(&mute)) break;
 		
 		set_mute(mute);
+		printf("M%d\n", is_muted());
+	}
+		break;
+	case 'S':
+	{
+		uint16_t shorted;
+		if (next_arg_unsigned(&shorted)) break;
+		
+		set_short(shorted);
+		printf("S%d\n", is_shorted());
 	}
 		break;
 	case 'B':