Bit-banged I2C implementation on any pin

doc/Doxyfile

@@ -610,7 +610,7 @@ WARN_LOGFILE           =
 # directories like "/usr/src/myproject". Separate the files or directories
 # with spaces.
 
-INPUT                  = ../libraries/FreetronicsLCD ../libraries/BlinkLED .
+INPUT                  = ../libraries/FreetronicsLCD ../libraries/BlinkLED ../libraries/BitBangI2C .
 
 # This tag can be used to specify the character encoding of the source files
 # that doxygen parses. Internally doxygen uses the UTF-8 encoding, which is

libraries/BitBangI2C/BitBangI2C.cpp

@@ -0,0 +1,216 @@
+/*
+ * Copyright (C) 2012 Southern Storm Software, Pty Ltd.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#include "BitBangI2C.h"
+#include <WProgram.h>
+
+/**
+ * \class BitBangI2C BitBangI2C.h <BitBangI2C.h>
+ * \brief Bit-banged implementation of an I2C master.
+ *
+ * This class implements the I2C master protocol on any arbitrary pair
+ * of data and clock pins.  It is not restricted to pre-defined pins as
+ * is the case for the standard \c Wire library.
+ *
+ * This implementation only implements the master side of the protocol.
+ * It assumes that there is a single bus master, no arbitration, and
+ * no clock stretching.
+ */
+
+#define i2cDelay()  delayMicroseconds(5)
+
+/**
+ * \brief Constructs a new bit-banged I2C master on \a dataPin and \a clockPin.
+ */
+BitBangI2C::BitBangI2C(uint8_t dataPin, uint8_t clockPin)
+    : _dataPin(dataPin)
+    , _clockPin(clockPin)
+    , started(false)
+{
+    // Initially set the CLOCK and DATA lines to be outputs in the high state.
+    pinMode(_clockPin, OUTPUT);
+    pinMode(_dataPin, OUTPUT);
+    digitalWrite(_clockPin, HIGH);
+    digitalWrite(_dataPin, HIGH);
+}
+
+/**
+ * \typedef BitBangI2C::ack_t
+ * \brief Type that represents an I2C ACK or NACK indication.
+ */
+
+/**
+ * \var BitBangI2C::ACK
+ * \brief Indicates that an I2C operation was acknowledged.
+ */
+
+/**
+ * \var BitBangI2C::NACK
+ * \brief Indicates that an I2C operation was not acknowledged.
+ */
+
+/**
+ * \brief Transmits an I2C start condition on the bus.
+ *
+ * \sa startRead(), startWrite()
+ */
+void BitBangI2C::start()
+{
+    pinMode(_dataPin, OUTPUT);
+    if (started) {
+        // Already started, so send a restart condition.
+        digitalWrite(_dataPin, HIGH);
+        digitalWrite(_clockPin, HIGH);
+        i2cDelay();
+    }
+    digitalWrite(_dataPin, LOW);
+    i2cDelay();
+    digitalWrite(_clockPin, LOW);
+    i2cDelay();
+    started = true;
+}
+
+/**
+ * \brief Transmits an I2C stop condition on the bus.
+ */
+void BitBangI2C::stop()
+{
+    pinMode(_dataPin, OUTPUT);
+    digitalWrite(_dataPin, LOW);
+    digitalWrite(_clockPin, HIGH);
+    i2cDelay();
+    digitalWrite(_dataPin, HIGH);
+    i2cDelay();
+    started = false;
+}
+
+#define I2C_WRITE   0x00
+#define I2C_WRITE10 0xF0
+#define I2C_READ    0x01
+#define I2C_READ10  0xF1
+
+/**
+ * \brief Starts a write operation by sending a start condition and the I2C control byte.
+ *
+ * The \a address must be the 7-bit or 10-bit address of the I2C slave
+ * on the bus.
+ *
+ * Returns BitBangI2C::ACK or BitBangI2C::NACK to indicate whether the
+ * read operation was acknowledged by the slave or not.
+ *
+ * \sa startWrite()
+ */
+BitBangI2C::ack_t BitBangI2C::startWrite(unsigned int address)
+{
+    start();
+    if (address < 0x80) {
+        // 7-bit address.
+        return write((uint8_t)((address << 1) | I2C_WRITE));
+    } else {
+        // 10-bit address.
+        if (write((uint8_t)(((address >> 7) & 0x06)) | I2C_WRITE10) == NACK)
+            return NACK;
+        return write((uint8_t)address);
+    }
+}
+
+/**
+ * \brief Starts a read operation by sending the start condition and the I2C control byte.
+ *
+ * The \a address must be the 7-bit or 10-bit address of the I2C slave
+ * on the bus.
+ *
+ * Returns BitBangI2C::ACK or BitBangI2C::NACK to indicate whether the
+ * read operation was acknowledged by the slave or not.
+ *
+ * \sa startWrite()
+ */
+BitBangI2C::ack_t BitBangI2C::startRead(unsigned int address)
+{
+    start();
+    if (address < 0x80) {
+        // 7-bit address.
+        return write((uint8_t)((address << 1) | I2C_READ));
+    } else {
+        // 10-bit address.
+        if (write((uint8_t)(((address >> 7) & 0x06)) | I2C_READ10) == NACK)
+            return NACK;
+        return write((uint8_t)address);
+    }
+}
+
+/**
+ * \brief Writes a single byte \a value on the I2C bus.
+ *
+ * Returns BitBangI2C::ACK or BitBangI2C::NACK to indicate whether the
+ * slave acknowledged the byte or not.
+ */
+BitBangI2C::ack_t BitBangI2C::write(uint8_t value)
+{
+    uint8_t mask = 0x80;
+    while (mask != 0) {
+        writeBit((value & mask) != 0);
+        mask >>= 1;
+    }
+    return readBit();
+}
+
+/**
+ * \brief Reads a single byte from the I2C bus.
+ *
+ * If \a ack is BitBangI2C::ACK, then the byte is acknowledged.  Otherwise
+ * the byte will not be acknowledged.
+ */
+uint8_t BitBangI2C::read(ack_t ack)
+{
+    uint8_t value = 0;
+    for (uint8_t bit = 0; bit < 8; ++bit)
+        value = (value << 1) | readBit();
+    writeBit(ack);
+    return value;
+}
+
+void BitBangI2C::writeBit(bool bit)
+{
+    pinMode(_dataPin, OUTPUT);
+    if (bit)
+        digitalWrite(_dataPin, HIGH);
+    else
+        digitalWrite(_dataPin, LOW);
+    i2cDelay();
+    digitalWrite(_clockPin, HIGH);
+    i2cDelay();
+    digitalWrite(_clockPin, LOW);
+    i2cDelay();
+}
+
+bool BitBangI2C::readBit()
+{
+    pinMode(_dataPin, INPUT);
+    digitalWrite(_dataPin, HIGH);
+    digitalWrite(_clockPin, HIGH);
+    bool bit = digitalRead(_dataPin);
+    i2cDelay();
+    digitalWrite(_clockPin, LOW);
+    i2cDelay();
+    return bit;
+}

libraries/BitBangI2C/BitBangI2C.h

@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2012 Southern Storm Software, Pty Ltd.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#ifndef BitBangI2C_h
+#define BitBangI2C_h
+
+#include <inttypes.h>
+
+class BitBangI2C {
+public:
+    BitBangI2C(uint8_t dataPin, uint8_t clockPin);
+
+    typedef bool ack_t;
+
+    static const ack_t ACK = false;
+    static const ack_t NACK = true;
+
+    void start();
+    void stop();
+
+    ack_t startWrite(unsigned int address);
+    ack_t startRead(unsigned int address);
+
+    ack_t write(uint8_t value);
+    uint8_t read(ack_t ack = ACK);
+
+private:
+    uint8_t _dataPin;
+    uint8_t _clockPin;
+    bool started;
+
+    void writeBit(bool bit);
+    bool readBit();
+};
+
+#endif