diff --git a/STM32F1/cores/maple/libmaple/usb/stm32f1/usb_cdcacm.c b/STM32F1/cores/maple/libmaple/usb/stm32f1/usb_cdcacm.c
index 7a5a772..774be42 100644
--- a/STM32F1/cores/maple/libmaple/usb/stm32f1/usb_cdcacm.c
+++ b/STM32F1/cores/maple/libmaple/usb/stm32f1/usb_cdcacm.c
@@ -384,9 +384,13 @@ void usb_cdcacm_enable(gpio_dev *disc_dev, uint8 disc_bit) {
     /* Present ourselves to the host. Writing 0 to "disc" pin must
      * pull USB_DP pin up while leaving USB_DM pulled down by the
      * transceiver. See USB 2.0 spec, section 7.1.7.3. */
-    gpio_set_mode(disc_dev, disc_bit, GPIO_OUTPUT_PP);
-    gpio_write_bit(disc_dev, disc_bit, 0);
-
+	 
+	if (disc_dev!=NULL)
+	{	 
+		gpio_set_mode(disc_dev, disc_bit, GPIO_OUTPUT_PP);
+		gpio_write_bit(disc_dev, disc_bit, 0);
+	}
+	
     /* Initialize the USB peripheral. */
     usb_init_usblib(USBLIB, ep_int_in, ep_int_out);
 }
@@ -395,7 +399,10 @@ void usb_cdcacm_disable(gpio_dev *disc_dev, uint8 disc_bit) {
     /* Turn off the interrupt and signal disconnect (see e.g. USB 2.0
      * spec, section 7.1.7.3). */
     nvic_irq_disable(NVIC_USB_LP_CAN_RX0);
-    gpio_write_bit(disc_dev, disc_bit, 1);
+	if (disc_dev!=NULL)
+	{
+		gpio_write_bit(disc_dev, disc_bit, 1);
+	}
 }
 
 void usb_cdcacm_putc(char ch) {
diff --git a/STM32F1/variants/generic_gd32f103c/board/board.h b/STM32F1/variants/generic_gd32f103c/board/board.h
index 50dd989..16295a1 100644
--- a/STM32F1/variants/generic_gd32f103c/board/board.h
+++ b/STM32F1/variants/generic_gd32f103c/board/board.h
@@ -70,8 +70,8 @@
 #define BOARD_JTDO_PIN            19
 #define BOARD_NJTRST_PIN          18
 
-#define BOARD_USB_DISC_DEV        GPIOB
-#define BOARD_USB_DISC_BIT        10
+#define BOARD_USB_DISC_DEV        NULL
+#define BOARD_USB_DISC_BIT        NULL
 
 // Note this needs to match with the PIN_MAP array in board.cpp
 enum {
diff --git a/STM32F1/variants/generic_stm32f103c/board/board.h b/STM32F1/variants/generic_stm32f103c/board/board.h
index 09351a6..4736dc9 100644
--- a/STM32F1/variants/generic_stm32f103c/board/board.h
+++ b/STM32F1/variants/generic_stm32f103c/board/board.h
@@ -70,8 +70,8 @@
 #define BOARD_JTDO_PIN            19
 #define BOARD_NJTRST_PIN          18
 
-#define BOARD_USB_DISC_DEV        GPIOB
-#define BOARD_USB_DISC_BIT        10
+#define BOARD_USB_DISC_DEV        NULL
+#define BOARD_USB_DISC_BIT        NULL
 
 #define LED_BUILTIN PC13
 
diff --git a/STM32F1/variants/generic_stm32f103r8/board/board.h b/STM32F1/variants/generic_stm32f103r8/board/board.h
index c274d64..36c2241 100644
--- a/STM32F1/variants/generic_stm32f103r8/board/board.h
+++ b/STM32F1/variants/generic_stm32f103r8/board/board.h
@@ -70,8 +70,8 @@
 #define BOARD_JTDO_PIN            19
 #define BOARD_NJTRST_PIN          18
 
-#define BOARD_USB_DISC_DEV        GPIOB
-#define BOARD_USB_DISC_BIT        10
+#define BOARD_USB_DISC_DEV        NULL
+#define BOARD_USB_DISC_BIT        NULL
 
 // Note this needs to match with the PIN_MAP array in board.cpp
 enum {
diff --git a/STM32F1/variants/nucleo_f103rb/board/board.h b/STM32F1/variants/nucleo_f103rb/board/board.h
index b27862d..5c7ece7 100644
--- a/STM32F1/variants/nucleo_f103rb/board/board.h
+++ b/STM32F1/variants/nucleo_f103rb/board/board.h
@@ -102,11 +102,8 @@
 /**
  * Note: there is no USB in this board.
  */
- // Roger Clark. These USB disconnect pin definitions have been added as a temporary fix in order that the this board compiles
- // following changes to add usb serial to other boards
- // I will remove them when the code in the core usb_serial.cpp has been tidied up so that they are no longer needed.
-#define BOARD_USB_DISC_DEV        GPIOB
-#define BOARD_USB_DISC_BIT        10
+#define BOARD_USB_DISC_DEV        NULL
+#define BOARD_USB_DISC_BIT        NULL
 
 /* Pin aliases: these give the GPIO port/bit for each pin as an
  * enum. These are optional, but recommended. They make it easier to