add Port_MCP23S18

src/Port_MCP23017.h

@@ -5,7 +5,7 @@
 #include <Wire.h>
 #include <PortInterface.h>
 
-/*
+/* Port_MCP23017
 write pins are connected to matrix Row (strobe pin) or LED.
 readPins are connected to matrix column to read which keys are pressed.
 

src/Port_MCP23018.h

@@ -1,7 +1,8 @@
 #ifndef PORT_MCP23018_H
 #define PORT_MCP23018_H
 #include "Port_MCP23017.h"
-/*
+
+/* Port_MCP23018
 write pins are connected to matrix Row (strobe pin) or LED.
 readPins are connected to matrix column to read which keys are pressed.
 

src/Port_MCP23S17.h

@@ -5,7 +5,7 @@
 #include <SPI.h>
 #include <PortInterface.h>
 
-/*
+/* Port_MCP23S17
 write pins are connected to matrix Row (strobe pin) or LED.
 readPins are connected to matrix column to read which keys are pressed.
 

src/Port_MCP23S18.h

@@ -0,0 +1,31 @@
+#ifndef PORT_MCP23S18_H
+#define PORT_MCP23S18_H
+#include "Port_MCP23S17.h"
+
+/* Port_MCP23S18 has not been tested.
+write pins are connected to matrix Row (strobe pin) or LED.
+readPins are connected to matrix column to read which keys are pressed.
+
+Port_MCP23S18 can only be active low (Scanner_IOE::activeState = LOW).
+Open-drain active high would not work because pull down resistors have no effect on sink.
+ https://en.wikipedia.org/wiki/Open_collector
+
+Use LED_PortOpenDrain class for indicator LEDs.
+
+Example instantiation:
+    const uint8_t IOE_ADDR = 0x20;              //MCP23S18 address pin grounded
+    Port_MCP23S18  portB(IOE_ADDR, 1, 0);       //all pins are set to output for strobes and LEDs
+    Port_MCP23S18  portA(IOE_ADDR, 0, 1<<0 | 1<<1 ); //pin 0 and pin 1 are set to input for reading,
+                                                //remaining pins can be used for LEDs
+Diode orientation
+ ----------------
+Diode orientation is explained in keybrd_library_user_guide.md > Diode orientation
+*/
+
+class Port_MCP23S18 : public Port_MCP23S17
+{
+    public:
+        Port_MCP23S18(const uint8_t deviceAddr, const uint8_t portNum, const uint8_t readPins)
+            : Port_MCP23S17(deviceAddr, portNum, readPins) {}
+};
+#endif

src/Port_PCA9655E.h

@@ -5,7 +5,7 @@
 #include <Wire.h>
 #include <PortInterface.h>
 
-/*
+/* Port_PCA9655E
 write pins are connected to matrix Row (strobe pin) or LED.
 readPins are connected to matrix column to read which keys are pressed.
 
@@ -29,9 +29,6 @@ Diode orientation
  ----------------
 Diode orientation is explained in keybrd_library_user_guide.md > Diode orientation
 
-PCA9655E data sheet
- ----------------
- http://www.onsemi.com/pub_link/Collateral/PCA9655E-D.PDF
 */
 
 class Port_PCA9655E : public PortInterface