diff --git a/src/Port_MCP23S17.cpp b/src/Port_MCP23S17.cpp
index 0a68660..1895596 100644
--- a/src/Port_MCP23S17.cpp
+++ b/src/Port_MCP23S17.cpp
@@ -12,11 +12,11 @@ uint8_t Port_MCP23S17::transfer(const uint8_t command, const uint8_t registerAdd
     uint8_t portState;                          //bit pattern
 
     SPI.beginTransaction( SPISettings(5000000, MSBFIRST, SPI_MODE0) ); //control SPI bus, 5 MHz
-    digitalWrite(SS, LOW);                      //enable Slave Select
+    digitalWrite(slaveSelect, LOW);             //enable Slave Select
     SPI.transfer(command);                      //write or read command
     SPI.transfer(registerAddr);                 //register address to write data to
     portState = SPI.transfer(data);             //write data, read portState
-    digitalWrite(SS, HIGH);                     //disable Slave Select
+    digitalWrite(slaveSelect, HIGH);                     //disable Slave Select
     SPI.endTransaction();
 
     return portState;
@@ -26,8 +26,8 @@ uint8_t Port_MCP23S17::transfer(const uint8_t command, const uint8_t registerAdd
 */
 void Port_MCP23S17::beginProtocol()
 {
-    pinMode(SS, OUTPUT);                        //configure controller's Slave Select pin to output
-    digitalWrite(SS, HIGH);                     //disable Slave Select
+    pinMode(slaveSelect, OUTPUT);               //configure controller's Slave Select pin to output
+    digitalWrite(slaveSelect, HIGH);            //disable Slave Select
     SPI.begin();
 }
 
@@ -39,13 +39,13 @@ void Port_MCP23S17::begin(const uint8_t activeState)
 {
     uint8_t pullUp;                             //bits, GPPU 0=pull-up disabled, 1=pull-up enabled
 
-    if (activeState == LOW)                        //if active low
+    if (activeState == LOW)                     //if active low
     {
-        pullUp = readPins;              //0=pull-up disabled (for LED), 1=pull-up enabled (for read)
+        pullUp = readPins;                      //0=pull-up disabled (for LED), 1=pull-up enabled (for read)
     }
     else                                        //if active high
     {
-        pullUp = 0;                         //0=pull-up disabled (for external pull-down resistors)
+        pullUp = 0;                             //0=pull-up disabled (for external pull-down resistors)
     }
 
     transfer(deviceAddr << 1, portNum, readPins); //configure IODIR
@@ -57,7 +57,7 @@ pin is bit pattern, where pin being set is 1.
 */
 void Port_MCP23S17::writeLow(const uint8_t pin)
 {
-    outputVal &= ~pin;                 //set pin output to low
+    outputVal &= ~pin;                          //set pin output to low
     transfer(deviceAddr << 1, portNum + 0x12, outputVal); //set GPIO port to outputVal
 }
 
@@ -66,7 +66,7 @@ pin is bit pattern, where pin being set is 1.
 */
 void Port_MCP23S17::writeHigh(const uint8_t pin)
 {
-    outputVal |= pin;                  //set pin output to high
+    outputVal |= pin;                           //set pin output to high
     transfer(deviceAddr << 1, portNum + 0x12, outputVal); //set GPIO port to outputVal
 }
 
diff --git a/src/Port_MCP23S17.h b/src/Port_MCP23S17.h
index 4130c17..0842a50 100644
--- a/src/Port_MCP23S17.h
+++ b/src/Port_MCP23S17.h
@@ -9,8 +9,7 @@
 write pins are connected to matrix Row (strobe pin) or LED.
 readPins are connected to matrix column to read which keys are pressed.
 
-Slave Select is hardcoded to Arduino Pin 10.
-Arduino Pin 10 avoids the speed penalty of digitalWrite.
+slaveSelect is Arduino-pin number connected to pin 11 (CS a.k.a. SS).
 
 Instantiation
  ------------
@@ -36,14 +35,15 @@ MCP23S17 data sheet
 class Port_MCP23S17 : public PortInterface
 {
     private:
+        const uint8_t slaveSelect;              //controller-pin number
         const uint8_t deviceAddr;
         const uint8_t portNum;                  //port identification number
         uint8_t outputVal;                      //bit pattern for strobe and LEDs
         const uint8_t readPins;                 //bit pattern, IODIR 0=output, 1=input
         uint8_t transfer(const uint8_t command, const uint8_t registerAddr, const uint8_t data);
     public:
-        Port_MCP23S17(const uint8_t deviceAddr, const uint8_t portNum, const uint8_t readPins)
-            : deviceAddr(deviceAddr), portNum(portNum), outputVal(0), readPins(readPins) {}
+        Port_MCP23S17(const uint8_t slaveSelect, const uint8_t deviceAddr, const uint8_t portNum, const uint8_t readPins)
+            : slaveSelect(slaveSelect), deviceAddr(deviceAddr), portNum(portNum), outputVal(0), readPins(readPins) {}
         void beginProtocol();
         void begin(const uint8_t activeState);
         virtual void writeLow(const uint8_t pin);
diff --git a/src/Port_ShiftRegs.h b/src/Port_ShiftRegs.h
index e464425..56167d2 100644
--- a/src/Port_ShiftRegs.h
+++ b/src/Port_ShiftRegs.h
@@ -6,7 +6,7 @@
 #include <PortWriteInterface.h>
 
 /* Port_ShiftRegs 
-slaveSelect is controller-pin number connected to shift register RCLK pin a.k.a. SS or ST
+slaveSelect is Arduino-pin number connected to shift register RCLK pin a.k.a. SS or ST
 */
 class Port_ShiftRegs : public PortWriteInterface
 {
diff --git a/tutorials/keybrd_5b_LED_on_IOE/keybrd_5b_LED_on_IOE.ino b/tutorials/keybrd_5b_LED_on_IOE/keybrd_5b_LED_on_IOE.ino
index 3be431d..c97062b 100644
--- a/tutorials/keybrd_5b_LED_on_IOE/keybrd_5b_LED_on_IOE.ino
+++ b/tutorials/keybrd_5b_LED_on_IOE/keybrd_5b_LED_on_IOE.ino
@@ -47,8 +47,9 @@ LED_uC LED_capsLck(21);
 
 // --------------- RIGHT SCANNER ---------------
 const uint8_t IOE_ADDR = 0x20;                  //MCP23S17 address, all 3 ADDR pins are grounded
-Port_MCP23S17 portA(IOE_ADDR, 0, 1<<0 | 1<<1 ); //for read
-Port_MCP23S17 portB(IOE_ADDR, 1, 0);            //for strobe
+const uint8_t slaveSelect = 10;
+Port_MCP23S17 portA(slaveSelect , IOE_ADDR, 0, 1<<0 | 1<<1 ); //for read
+Port_MCP23S17 portB(slaveSelect , IOE_ADDR, 1, 0);            //for strobe
 
 Scanner_IOE scanner_R(LOW, portB, portA);