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i2c.md

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I2C Master

An I2C master core.

Pins

  • SDA : Data I/O
  • SCL : Clock I/O

Note that both pins are bidirectional and have to be connected directly to FPGA GPIO pins in the FPGA definition.

Usage

Initialization

The core can either be initialized in standard or in fast mode:

myI2CMaster.init(I2CMaster.MODE_STANDARD);
myI2CMaster.init(I2CMaster.MODE_FAST);

In standard mode the clock frequency will be approx. 90 kHz, in fast mode 350 kHz. Calling the init() method without parameters defaults to the normal mode.

Transfer Data

For typical read and write operations, you can use the following methods:

void writeByte(int deviceAddress, int registerAddress, int data)
int readByte(int deviceAddress, int registerAddress)

The writeByte(...) method initiates three transfers:

  1. Start condition; Write device address
  2. Write register address
  3. Write data; Stop condition

The readByte(...) method performs a typical I2C four-transfer-read:

  1. Start condition; Write device address
  2. Write register address
  3. Repeated start condition; Write device address
  4. Read register content; Stop condition; Send nack

In case the slave device does not acknowledge any of the transfers, an I2CException will be thrown. Both methods use the generic transfer method that will now be introduced.

Generic Transfer Method

In case these shorthand methods can not be applied, there is also a generic transfer method giving full control of the core:

int transfer(int data, boolean write, Boolean start, boolean nack)

The method requires the following parameters:

  • data : 8 bits of data when writing data or 7 address bits plus the R/W bit (which is the LSB)
  • write : True, when writing data or address. False when reading. Then, the data parameter will then be ignored.
  • start : True, if the start condition should be asserted. False, if the stop condition should be asserted at the end of the transfer. If neither start nor stop condition should be asserted this parameter can be set to null.
  • nack : True, if a nack should be sent to indicate the end of a read transfer.

Note that the nack parameter can only be true for read transfers (write is false). For read transfers the method will return the value that has been received from a slave device. When writing (write is true), the method will return 1 if the transfer has been acknowledged by a slave and 0 if not.