diff --git a/doc/CHANGELOG.md b/doc/CHANGELOG.md
index d9b885d..5e5c172 100644
--- a/doc/CHANGELOG.md
+++ b/doc/CHANGELOG.md
@@ -6,6 +6,27 @@ This project adheres to [Semantic Versioning 2.0.0](http://semver.org/).
 keybrd version 0.x.x is for initial development.
 keybrd version 1.0.0 will be released when the public API is stable.
 
+0.6.4 (2016-11-16)
+------------------
+* Enhancements
+  * add Port_MCP23018
+  * add Port_MCP23S18
+  * add Port_ShiftRegs
+  * add PortWriteInterface
+  * add add LED_PortOpenDrain
+  * add examples/IOE_PCA9655E_development/
+  * rename strobeOn to activeState
+  * move strobe logic from Port_*::write() to Scanner_IOE::scan()
+
+* Backward incompatible changes
+  * rename print_microseconds_per_scan() to printMicrosecondsPerScan()
+  * rename print_scans_per_second() to printScansPerSecond()
+  * rename Scanner_ShiftRegsPISOSingleRow to Scanner_ShiftRegsRead
+  * rename Scanner_ShiftRegsPISOMultiRow to Scanner_ShiftRegsReadStrobed
+  * in Scanner_ShiftRegsReadStrobed, reverse slaveSelect HIGH/LOW for SPI compatible tri-state
+  * in Port_MCP23S17, add slaveSelect to constructor parameter
+  * in Port_*, replace write() with writeHigh() and writeLow()
+
 0.6.3 (2016-10-06)
 ------------------
 * Enhancements
diff --git a/examples/IOE_PCA9655E_development/README.md b/examples/IOE_PCA9655E_development/README.md
index 1cc7994..e7464f3 100644
--- a/examples/IOE_PCA9655E_development/README.md
+++ b/examples/IOE_PCA9655E_development/README.md
@@ -1,4 +1,4 @@
-The series of sketches in this folder where used to develope the Port_PCA9655E class.
+The series of sketches in this folder where used to develop the Port_PCA9655E class in stages.
 The folder numbers are ordered from fundamental to practical.
 
 Each sketch was tested on a breadboard.  Breadboards hold:
diff --git a/src/Port_MCP23017.cpp b/src/Port_MCP23017.cpp
index ea0a93d..cc88e45 100644
--- a/src/Port_MCP23017.cpp
+++ b/src/Port_MCP23017.cpp
@@ -19,13 +19,13 @@ void Port_MCP23017::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)
     }
     else                                        //if active high
     {
-        pullUp = 0;                         //0=pull-up disabled (for external pull-down resistors)
+        pullUp = 0;                             //0=pull-up disabled (external pull-down resistors)
     }
 
     Wire.beginTransmission(deviceAddr);
@@ -44,7 +44,7 @@ pin is bit pattern, where pin being set is 1.
 */
 void Port_MCP23017::writeLow(const uint8_t pin)
 {
-    outputVal &= ~pin;                 //set pin output to low
+    outputVal &= ~pin;                          //set pin output to low
 
     Wire.beginTransmission(deviceAddr);
     Wire.write(portNum + 0x12);                 //GPIO
@@ -72,7 +72,7 @@ uint8_t Port_MCP23017::read()
 {
     Wire.beginTransmission(deviceAddr);
     Wire.write(portNum + 0x12);                 //GPIO
-    Wire.endTransmission(false);                //MCP23017 needs false to send a restart ??todo really?
+    Wire.endTransmission(false);                //MCP23017 needs false to send a restart
 
     Wire.requestFrom(deviceAddr, 1u);           //request one byte from input port
 
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 c97062b..43a3d48 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
@@ -47,7 +47,7 @@ LED_uC LED_capsLck(21);
 
 // --------------- RIGHT SCANNER ---------------
 const uint8_t IOE_ADDR = 0x20;                  //MCP23S17 address, all 3 ADDR pins are grounded
-const uint8_t slaveSelect = 10;
+const uint8_t slaveSelect = 10;                 //Arduino-pin number connected to MCP23S17 CS or SS
 Port_MCP23S17 portA(slaveSelect , IOE_ADDR, 0, 1<<0 | 1<<1 ); //for read
 Port_MCP23S17 portB(slaveSelect , IOE_ADDR, 1, 0);            //for strobe
 
@@ -136,7 +136,7 @@ so that scanner's ports can turn on LayerState_LED's default-layer LED.
 void setup()
 {
     scanner_R.begin();
-    layerState.begin();               //todo call LayerState_LED::begin() after Scanner_IOE::begin()
+    layerState.begin();               //call LayerState_LED::begin() after Scanner_IOE::begin()
 }
 
 void loop()
diff --git a/tutorials/tutorial_10_writing_IOE_port_classes.md b/tutorials/tutorial_10_writing_IOE_port_classes.md
index e2f23b7..4c81352 100644
--- a/tutorials/tutorial_10_writing_IOE_port_classes.md
+++ b/tutorials/tutorial_10_writing_IOE_port_classes.md
@@ -19,7 +19,9 @@ Steps to writing a new port class:
 5. Study other keybrd port classes.
  * SPI I/O expander port classes: Port_MCP23S17
  * I2C I/O expander port classes: Port_PCA9655E 
-6. Write the port classes for your I/O expander.  Debugging I/O expander code is hard because
+6. Write the port classes for your I/O expander.
+ * [Example](../examples/IOE_PCA9655E_development/) shows how Port_PCA9655E was developed in stages, from fundamental to practical
+ * Debugging I/O expander code is hard because
    SPI or I2C protocol, expander configuration, and expander commands.
 
 <br>