I2C Interface

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Detailed Description

Implementation for communicating with I2C slaves using a polled I2C master implementation

Handles I2C communications with external I2C devices. Also called TWI (two wire interface), Find the i2c specification at http://www.philips.com.

Devices are connected to two port pins on the chip. The i2c bus uses two signals SCK - clock and SDA - Data. Lines are active low and devices are ANDED together on the bus using open collector or open drain.

The internal pull up resistors in the AVR are used so no external pull up resistors are needed. Code has not been tested with multiple masters; the bus arbitration is not tested.

Hardware configuration is done in hardware.h. The following macros are needed by i2c.c:

• I2C_RELEASE_SDA() - Release the SDA line to a high state
• I2C_RELEASE_SCL() - Release the SCL line to a high state
• I2C_DRIVE_SDA() - Drive the SDA to a low state
• I2C_DRIVE_SCL() - Drive the SCL to a low state
• I2C_IS_SDA_RELEASED() - Returns !0 if SDA line is released, 0 if SDA is driven (low)
• I2C_IS_SCL_RELEASED() - Returns !0 if SCL line is released, 0 if SCL is driven (low)

First startbit, then slave address including LSB (read/write) then either a byte send or byte read. Send bytes to LCD example:

  I2C_SendStartBit();
  I2C_SendByte(LCD_DRIVER_ADDRESS); //I2C slave address
  I2C_SendByte(LCD_CONTROL_BYTE_WRITE_COMMAND);  //This address LCD control bytes
  I2C_SendByte(LCD_SET_DDRAM_ADDRESS(LCD_GET_DDRAM_ADDR(x,y)));
  I2C_SendStopBit();

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Files

• file i2c.c
• file i2c.h

Functions

• void I2C_Init (void)
• void I2C_SendStartBit (void)
• bool I2C_SendByte (uint8_t byte)
• uint8_t I2C_GetByte (bool lastbyte)
• void I2C_SendStopBit (void)

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Function Documentation

void I2C_Init (  void   )  [inline]

Initialize the I2C port pins.

void I2C_SendStartBit (  void   )

Send a start bit Start bit is a 1 to 0 transition on SDA while SCL is high ________ SDA master \________ _________________ SDA slave ___/ __________ SCL ___/ \_____

bool I2C_SendByte (  uint8_t  byte  )

Send a byte (address or data) to the slave parameter order used to select between sending LSB or MSB first Parameters: byte  Byte to send to slave Return values: 1  if the slave did 0  if the slave didn't ack. __________________________ ________ SDA slave \____/ .. ack ___ ___ ___ ___ __________ ___ ___ SDA master ___/___X___X___..X___X___/ \___x___.. _ _ _ _ _ _ _ _ SCL ____/1\_/2\_/3\.._/7\_/8\_/9\____/1\_/2\.. msb lsb ack ^ | [Can be held low by slave] See also: I2C_SendStartBit I2C_SendStopBit

uint8_t I2C_GetByte (  bool  lastbyte  )

Reads a byte from the slave Parameters: lastbyte  1 if last byte read 0 if more bytes to be read Returns: byte read from slave _____________________ __________ SDA master __/ \____/ .. ack _______ ___ ___ ___ ______________ ___ SDA slave \__X___X___..X___X___/ \___x___.. _ _ _ _ _ _ _ _ SCL ____/1\_/2\_/3\.._/7\_/8\_/9\____/1\_/2\.. msb lsb ack

void I2C_SendStopBit (  void   )

Generates a stop bit assumes SCL is low Stop bit is a 0 to 1 transition on SDA while SCL is high ____ SDA _____/ ______ SCL ___/ See also: I2C_SendStartBit I2C_SendByte

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