Update README.md

README.md

@@ -11,7 +11,8 @@ This library provides full control over the Microchip's [MCP23017](https://www.m
  * Full interrupt support
 
 ## Usage
-Unlike most Arduino library, no default instance is created when the library is included. It's up to you to create one with the appropriate chip I2C address.
+Unlike most Arduino library, no default instance is created when the library is included. It's up to you to create one using the appropriate I2C address based on  MCP23017 `A0`, `A1` and `A2` pins wirings.
+Available addresses go from `0x20` to `0x27`, allowing up to 8 MCP23017 on the same I2C bus.
 
 ```cpp
 #include <Arduino.h>
@@ -23,7 +24,11 @@ MCP23017 mcp = MCP23017(0x24);
 Additionaly, you can specify the `Wire` instance to use as a second argument. For instance `MCP23017(0x24, Wire1)`.  
 See included examples for further usage.
 
-## Remarks
+## Warning about GPA7 & GPB7
+
+GPA7 or GPB7 should not be used as inputs despite what the configuration registers allow. As [stated by Microchip](https://microchip.my.site.com/s/article/GPA7---GPB7-Cannot-Be-Used-as-Inputs-In-MCP23017), it can lead to SDA signal corruption or even malfunction in the host bus under some conditions.
+
+## Breaking changes in v2.0.0
 Major renames have been performed in v2.0.0 to improve compatibility with a variety of platforms. Existing code *will* break when you update from version v1.x.
 
 | Name in v1.x          | Name in v2.x              |
@@ -32,4 +37,4 @@ Major renames have been performed in v2.0.0 to improve compatibility with a vari
 | `MCP23017_REGISTER`   | `MCP23017Register`        |
 | `MCP23017_INTMODE`    | `MCP23017InterruptMode`   |
 
-In addition to this, every member of the `MCP23017Register` enum were renamed to avoid possible conflicts with macro definitions. `GPIOA` was renamed to `GPIO_A`, `INTCAPA` to `INTCAP_A` and so on...
+In addition to this, every member of the `MCP23017Register` enum were renamed to avoid possible conflicts with macro definitions. `GPIOA` was renamed to `GPIO_A`, `INTCAPA` to `INTCAP_A` and so on...

examples/PortCopy/PortCopy.ino

@@ -1,8 +1,8 @@
 /**
  * On every loop, the state of the port B is copied to port A.
  *
- * Use active low inputs on port A. Internal pullups are enabled by default by the library so there is no need for external resistors.
- * Place LEDS on port B for instance. 
+ * Use active low inputs on port B. Internal pullups are enabled by default by the library so there is no need for external resistors.
+ * Place LEDS on port A for instance. 
  * When pressing a button, the corresponding led is shut down.
  * 
  * You can also uncomment one line to invert the input (when pressing a button the corresponding led is lit)
@@ -35,4 +35,4 @@ void loop() {
 
     currentB = mcp.readPort(MCP23017Port::B);
     mcp.writePort(MCP23017Port::A, currentB);
-}
+}

src/MCP23017.cpp

@@ -5,6 +5,11 @@ MCP23017::MCP23017(uint8_t address, TwoWire& bus) {
 	_bus = &bus;
 }
 
+MCP23017::MCP23017(TwoWire& bus) {
+	_deviceAddr = MCP23017_I2C_ADDRESS;
+	_bus = &bus;
+}
+
 MCP23017::~MCP23017() {}
 
 void MCP23017::init()
@@ -14,12 +19,23 @@ void MCP23017::init()
 	//SEQOP = 	1 : sequential operation disabled, address pointer does not increment
 	//DISSLW = 	0 : slew rate enabled
 	//HAEN = 	0 : hardware address pin is always enabled on 23017
-	//ODR = 	0 : open drain output
+	//ODR = 	0 : active driver output (INTPOL bit sets the polarity.)
+
 	//INTPOL = 	0 : interrupt active low
+	//UNIMPLMENTED 	0 : unimplemented: Read as ‘0’
+
 	writeRegister(MCP23017Register::IOCON, 0b00100000);
+}
 
-	//enable all pull up resistors (will be effective for input pins only)
-	writeRegister(MCP23017Register::GPPU_A, 0xFF, 0xFF);
+void MCP23017::begin()
+{
+	init();
+}
+
+void MCP23017::begin(uint8_t address)
+{
+	_deviceAddr = address;
+	begin();
 }
 
 void MCP23017::portMode(MCP23017Port port, uint8_t directions, uint8_t pullups, uint8_t inverted)

src/MCP23017.h

@@ -3,6 +3,7 @@
 #include <Arduino.h>
 #include <Wire.h>
 
+#define MCP23017_I2C_ADDRESS 0x20    ///< The default I2C address of MCP23017.
 #define _MCP23017_INTERRUPT_SUPPORT_ ///< Enables support for MCP23017 interrupts.
 
 enum class MCP23017Port : uint8_t
@@ -11,6 +12,28 @@ enum class MCP23017Port : uint8_t
 	B = 1
 };
 
+struct MCP23017Pin
+{
+	enum Names {
+		GPA0 = 0,
+		GPA1,
+		GPA2,
+		GPA3,
+		GPA4,
+		GPA5,
+		GPA6,
+		GPA7,
+		GPB0 = 8,
+		GPB1,
+		GPB2,
+		GPB3,
+		GPB4,
+		GPB5,
+		GPB6,
+		GPB7
+	};
+};
+
 /**
  * Controls if the two interrupt pins mirror each other.
  * See "3.6 Interrupt Logic".
@@ -65,10 +88,24 @@ class MCP23017
 	 * Instantiates a new instance to interact with a MCP23017 at the specified address.
 	 */
 	MCP23017(uint8_t address, TwoWire& bus = Wire);
+	/**
+	 * Instantiates a new instance to interact with a MCP23017 at the
+	 * MCP23017_I2C_ADDRESS default.
+	 */
+	MCP23017(TwoWire& bus = Wire);
 	~MCP23017();
 #ifdef _DEBUG
 	void debug();
 #endif
+	/**
+	 * Uses the I2C address set during construction. Implicitly calls init().
+	 */
+	void begin();
+	/**
+	 * Overrides the I2C address set by the constructor. Implicitly calls begin().
+
+	 */
+	void begin(uint8_t address);
 	/**
 	 * Initializes the chip with the default configuration.
 	 * Enables Byte mode (IOCON.BANK = 0 and IOCON.SEQOP = 1).
@@ -191,8 +228,8 @@ class MCP23017
 
 	/**
 	 * Controls how the interrupt pins act with each other.
-	 * If intMode is SEPARATED, interrupt conditions on a port will cause its respective INT pin to active.
-	 * If intMode is OR, interrupt pins are OR'ed so an interrupt on one of the port will cause both pints to active.
+	 * If intMode is Separated, interrupt conditions on a port will cause its respective INT pin to active.
+	 * If intMode is Or, interrupt pins are OR'ed so an interrupt on one of the port will cause both pints to active.
 	 * 
 	 * Controls the IOCON.MIRROR bit. 
 	 * See "3.5.6 Configuration register".
@@ -221,4 +258,4 @@ class MCP23017
 	void clearInterrupts(uint8_t& portA, uint8_t& portB);
 
 #endif
-};
+};