diff --git a/arch/arm/src/lpc214x/lpc214x_usbdev.c b/arch/arm/src/lpc214x/lpc214x_usbdev.c
index 31098a6e7fc..9ab55b79e85 100644
--- a/arch/arm/src/lpc214x/lpc214x_usbdev.c
+++ b/arch/arm/src/lpc214x/lpc214x_usbdev.c
@@ -787,7 +787,9 @@ static void lpc214x_epwrite(ubyte epphy, const ubyte *data, uint32 nbytes)
   uint32 value;
   boolean aligned = (((uint32)data & 3) == 0);
 
-  /* Set the write enable bit for this physical EP address */
+  /* Set the write enable bit for this physical EP address. Bits 2-5 are
+   * the logical endpoint number (0-15)
+   */
 
   lpc214x_putreg(((epphy << 1) & LPC214X_USBCTRL_EPMASK) | LPC214X_USBCTRL_WREN,
                  LPC214X_USBDEV_CTRL);
@@ -865,7 +867,9 @@ static int lpc214x_epread(ubyte epphy, ubyte *data, uint32 nbytes)
         }
     }
 
-  /* Set the read enable bit for this physical EP address */
+  /* Set the read enable bit for this physical EP address.  Bits 2-5 are
+   * the logical endpoint number (0-15).
+   */
 
   lpc214x_putreg(((epphy << 1) & LPC214X_USBCTRL_EPMASK) | LPC214X_USBCTRL_RDEN,
                  LPC214X_USBDEV_CTRL);
diff --git a/arch/arm/src/lpc214x/lpc214x_usbdev.h b/arch/arm/src/lpc214x/lpc214x_usbdev.h
index 55438799e74..9ed2550a859 100644
--- a/arch/arm/src/lpc214x/lpc214x_usbdev.h
+++ b/arch/arm/src/lpc214x/lpc214x_usbdev.h
@@ -185,9 +185,9 @@
 
 /* USB Control register bit definitions */
 
-#define LPC214X_USBCTRL_RDEN         (0x00000001)
-#define LPC214X_USBCTRL_WREN         (0x00000002)
-#define LPC214X_USBCTRL_EPMASK       (0x0000003c)
+#define LPC214X_USBCTRL_RDEN         (0x00000001) /* Bit 0=1: Read is enabled */
+#define LPC214X_USBCTRL_WREN         (0x00000002) /* Bit 0=1: Write is enabled */
+#define LPC214X_USBCTRL_EPMASK       (0x0000003c) /* Bits 2:5: Logical endpoint 0-15 */
 
 /* Endpoints *******************************************************************/