diff --git a/mk4-bootloader/Core/Inc/main.h b/mk4-bootloader/Core/Inc/main.h
index 0a64c0c..5e2d75d 100644
--- a/mk4-bootloader/Core/Inc/main.h
+++ b/mk4-bootloader/Core/Inc/main.h
@@ -66,6 +66,7 @@ extern "C" {
 #define bSegDecode7 0b0000011100
 #define bSegDecode8 0b0111111100
 #define bSegDecode9 0b0110111100
+#define bSegDecodeU 0b0011111000
 
 #define bCat0 0b1111000000000000
 #define bCat1 0b1110001000000000
@@ -94,6 +95,9 @@ extern "C" {
 
 #define ERR_UNKNOWN               bSegDecode9
 
+// User request bootloader hang for backup USB stack
+#define ERR_USER                  bSegDecodeU
+
 /* USER CODE END EC */
 
 /* Exported macro ------------------------------------------------------------*/
diff --git a/mk4-bootloader/Core/Src/main.c b/mk4-bootloader/Core/Src/main.c
index 70d91d6..046ec18 100644
--- a/mk4-bootloader/Core/Src/main.c
+++ b/mk4-bootloader/Core/Src/main.c
@@ -402,6 +402,11 @@ int main(void)
 // debug force reload
 // new_fw_crc=0;
 
+  // Hinge TX connection shorted to ground - force bootloader to hang
+  if ((GPIOA->IDR & (1<<2))==0) {
+    hang_error(ERR_USER);
+  }
+
 
   if (loaded_fw_crc == byteswap32(*(uint32_t*)(FLASH_BASE + BOOT_SIZE + APP_SIZE -4)) ) { // loaded firmware valid
 
@@ -717,6 +722,15 @@ static void MX_GPIO_Init(void)
   GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
   HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
 
+  /**USART2 GPIO Configuration
+  PA2     ------> USART2_TX
+  PA3     ------> USART2_RX
+  */
+  GPIO_InitStruct.Pin = GPIO_PIN_2;
+  GPIO_InitStruct.Mode = GPIO_MODE_INPUT;
+  GPIO_InitStruct.Pull = GPIO_PULLUP;
+  HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
+
   /*Configure GPIO pin Output Level */
   HAL_GPIO_WritePin(GPIOC, GPIO_PIN_13|GPIO_PIN_0|GPIO_PIN_1|GPIO_PIN_2
                           |GPIO_PIN_3|GPIO_PIN_4|GPIO_PIN_5|GPIO_PIN_6