diff --git a/arch/arm/src/xmc4/xmc4_clockutils.c b/arch/arm/src/xmc4/xmc4_clockutils.c
index 4d334eaef53..2a391ca3861 100644
--- a/arch/arm/src/xmc4/xmc4_clockutils.c
+++ b/arch/arm/src/xmc4/xmc4_clockutils.c
@@ -161,6 +161,7 @@ uint32_t xmc4_get_coreclock(void)
 uint32_t xmc4_get_periphclock(void)
 {
   uint32_t periphclock;
+  uint32_t regval;
 
   /* Get the CPU clock frequency.  Unless it is divided down, this also the
    * peripheral clock frequency.
@@ -170,12 +171,12 @@ uint32_t xmc4_get_periphclock(void)
 
   /* Get the peripheral clock divider */
 
-  periphclock = getreg32(XMC4_SCU_PBCLKCR);
-  if ((periphclock & SCU_PBCLKCR_PBDIV) != 0)
+  regval = getreg32(XMC4_SCU_PBCLKCR);
+  if ((regval & SCU_PBCLKCR_PBDIV) != 0)
     {
       /* The peripheral clock is fCPU/2 */
 
-      periphclock <<= 1;
+      periphclock >>= 1;
     }
 
   return periphclock;
diff --git a/arch/arm/src/xmc4/xmc4_gpio.c b/arch/arm/src/xmc4/xmc4_gpio.c
index e26967f06f3..b104def53c3 100644
--- a/arch/arm/src/xmc4/xmc4_gpio.c
+++ b/arch/arm/src/xmc4/xmc4_gpio.c
@@ -234,7 +234,7 @@ static inline void xmc4_gpio_hwsel(uintptr_t portbase, unsigned int pin,
  ****************************************************************************/
 
 static inline void xmc4_gpio_pdisc(uintptr_t portbase, unsigned int pin,
-                                   bool value)
+                                   bool enable)
 {
   uint32_t regval;
   uint32_t mask;
@@ -243,16 +243,21 @@ static inline void xmc4_gpio_pdisc(uintptr_t portbase, unsigned int pin,
 
   regval = xmc4_gpio_getreg(portbase, XMC4_PORT_PDISC_OFFSET);
 
-  /* Set/clear the enable/disable (or analg) value for this field */
+  /* Set or clear the pin field in the PDISC register.
+   *
+   * Disable = set
+   * Analog  = set
+   * Enable = clear
+   */
 
   mask = PORT_PIN(pin);
-  if (value)
+  if (enable)
     {
-      regval |= mask;
+      regval &= ~mask;
     }
   else
     {
-      regval &= ~mask;
+      regval |= mask;
     }
 
   xmc4_gpio_putreg(portbase, XMC4_PORT_PDISC_OFFSET, regval);
diff --git a/arch/arm/src/xmc4/xmc4_usic.c b/arch/arm/src/xmc4/xmc4_usic.c
index dd69cf318dd..1b82b9e16d5 100644
--- a/arch/arm/src/xmc4/xmc4_usic.c
+++ b/arch/arm/src/xmc4/xmc4_usic.c
@@ -121,12 +121,12 @@ int xmc4_enable_usic(enum usic_e usic)
 
             putreg32(SCU_CGAT0_USIC0, XMC4_SCU_CGATCLR0);
 
-            /* De-assert peripheral reset USIC0 */
+            /* Set bit in PRCLR0 to de-assert USIC0 peripheral reset */
 
             putreg32(SCU_PR0_USIC0RS, XMC4_SCU_PRCLR0);
           }
 #else
-        /* De-assert peripheral reset USIC0 */
+        /* Set bit in PRCLR0 to de-assert USIC0 peripheral reset */
 
         putreg32(SCU_PR0_USIC0RS, XMC4_SCU_PRCLR0);
 #endif
@@ -143,12 +143,12 @@ int xmc4_enable_usic(enum usic_e usic)
 
             putreg32(SCU_CGAT1_USIC1, XMC4_SCU_CGATCLR1);
 
-            /* De-assert peripheral reset USIC1 */
+            /* Set bit in PRCLR1 to de-assert USIC1 peripheral reset */
 
             putreg32(SCU_PR1_USIC1RS, XMC4_SCU_PRCLR1);
           }
 #else
-        /* De-assert peripheral reset USIC1 */
+        /* Set bit in PRCLR1 to de-assert USIC1 peripheral reset */
 
         putreg32(SCU_PR1_USIC1RS, XMC4_SCU_PRCLR1);
 #endif
@@ -165,12 +165,12 @@ int xmc4_enable_usic(enum usic_e usic)
 
             putreg32(SCU_CGAT1_USIC2, XMC4_SCU_CGATCLR1);
 
-            /* De-assert peripheral reset USIC2 */
+            /* Set bit in PRCLR1 to de-assert USIC2 peripheral reset */
 
             putreg32(SCU_PR1_USIC2RS, XMC4_SCU_PRCLR1);
           }
 #else
-        /* De-assert peripheral reset USIC2 */
+        /* Set bit in PRCLR1 to de-assert USIC2 peripheral reset */
 
         putreg32(SCU_PR1_USIC2RS, XMC4_SCU_PRCLR1);
 #endif
@@ -203,7 +203,7 @@ int xmc4_disable_usic(enum usic_e usic)
   switch (usic)
     {
       case USIC0:
-        /* Assert peripheral reset USIC0 */
+        /* Set bit in PRSET0 to assert USIC0 peripheral reset */
 
         putreg32(SCU_PR0_USIC0RS, XMC4_SCU_PRSET0);
 
@@ -216,7 +216,7 @@ int xmc4_disable_usic(enum usic_e usic)
 
 #if XMC4_NUSIC > 1
       case USIC1:
-        /* Assert peripheral reset USIC0 */
+        /* Set bit in PRSET1 to assert USIC1 peripheral reset */
 
         putreg32(SCU_PR1_USIC1RS, XMC4_SCU_PRSET1);
 
@@ -229,7 +229,7 @@ int xmc4_disable_usic(enum usic_e usic)
 
 #if XMC4_NUSIC > 2
       case USIC2:
-        /* Assert peripheral reset USIC0 */
+        /* Set bit in PRSET1 to assert USIC2 peripheral reset */
 
         putreg32(SCU_PR1_USIC2RS, XMC4_SCU_PRSET1);
 
diff --git a/configs/xmc4500-relax/README.txt b/configs/xmc4500-relax/README.txt
index 0ee63341d44..c6d014b6665 100644
--- a/configs/xmc4500-relax/README.txt
+++ b/configs/xmc4500-relax/README.txt
@@ -14,11 +14,13 @@ Serial Console
   The RX and TX pins is available:
   
     RX     - P1.4, Connector X2, pin 17
-    TX     - P1.5, Connector X2, pin 17
+    TX     - P1.5, Connector X2, pin 16
     GND    -       Available on pins 1-4 of either connector X1 or X2
     VDD3.3 -       Available on pins 37-38 of either connector X1 or X2
     VDD5   -       Available on pins 39-40 of either connector X1 or X2
 
+  A TTL to RS-232 convertor or a USB TTL-to-USB serial adaptor is required.
+
 LEDs
 ====