Component: I2C Master (Comms: Interface)

Author	Matrix Ltd.
Version	1.4
Category	Comms: Interface

I2C Master component

Generic Two Wire I2C Communications Interface

Detailed description

Overview

The I2C bus is a medium speed communications bus which is usually best suited for talking between devices situated on the same circuit board. Due to the high frequency digital nature of the bus care should be taken to keep tracks as short as possible and as far away as possible from other sources of noise. A typical I2C bus consists of two signals, data and clock. The I2C bus usually consists of a single master device and then one or more slave devices. The master device initiates all the communications and can only communicate with a single device on the bus at a time by sending a unique device address as the first byte.

Each I2C transaction consists of a start and a stop as well as one or more data bytes made up of 8 clock cycles allowing the 8-bits of each byte to be transferred. Each byte send is followed by an Ack (acknowledged) or a Nak (not acknowledged) from the receiving device.

Pull up resistors

The I2C bus usually requires pull up resistors in the range of 4.7K to 10K between the two I2C signals and VCC. Some I2C devices have the pull up resistors built in so as to avoid external components.

The pull up resistors can be useful when interfacing a 5V microcontroller to a 3V3 sensor as the pull up resistor can be connected to 3V3 to eliminate the need for voltage level shifting.

Start / Restart / Stop

The Start, Restart and Stop operations are each states which the bus can be put into using the I2C specification.

Generic Write Transaction

A generic write transaction to a memory device might look something like this:

Start

Send External Device Address Byte (Write mode)

Send Internal Address Byte

Send Data Byte

Stop

Generic Read Transaction

A generic read transaction to a memory device might look something like this:

Start

Send External Device Address Byte (Write mode)

Send Internal Address Byte

Restart

Send External Device Address Byte (Read mode)

Read Data Byte

Stop

Examples

More information on I2C can be found here,

Matrix Flowcode Blog: Simplified communications I2C and SPI

Generic I2C EEPROM

Example file demonstrating how to read and write bytes from a generic I2C EEPROM device. I2CEEPROM

Simulated I2C devices

This example uses the I2C master component combined with the DS1307 injector to simulate an I2C communications bus between the target Microcontroller and the virtual DS1307 device. I2C DS1307 Example The panel displays the current time from the DS1307 RAM which is populated to match the system time.

The I2C console shows the communications between the target microcontroller and simulated I2C device.

The DS1307 console shows the contents of RAM memory on the simulated I2C device.

Downloadable macro reference

	ReceiveByte
Receives a byte from the I²C bus.
- BYTE	Last
Used to signify the last byte when streaming incoming data. 0=Not last byte, 1=Last Byte
- BYTE	Return

	Restart
Outputs a restart condition onto the I²C bus.
- VOID	Return

	Stop
Outputs a stop condition onto the I²C bus.
- VOID	Return

	Transaction_Write
Attempt to write Length number of bytes to the I2C slave from the given Buffer. Ensure that the Buffer is large enough. Returns the number of bytes written, the caller should check that this matches requested Length
- BYTE	Buffer
Buffer of bytes to write to the I2C
- UINT	Length
Number of bytes to send out, MS bit 0x8000 signifies no Stop if set
- UINT	Return

	TransmitByte
Sends a byte on the I²C bus. Returns the acknowledge if any. 0 represents that data was acknowledged and 1 represents no acknowledge was detected.
- BYTE	Data
Data byte to send on the I²C bus.
- BYTE	Return

	GenericWriteRegister
Function to perform a generic I2C Write transaction. The 7-bit device ID is automatically shifted up by one bit to make room for the read/write bit.
- BYTE	Device_ID
7-bit Device Address ID
- UINT	Address
- BYTE	Data
Data Byte
- BYTE	AddressByteCount
Specifies the number of address bytes, Range: 1 or 2
- VOID	Return

	Transaction_Uninit
Uninitialise the I2C interface
- VOID	Return

	GenericReadRegister
Function to perform a generic I2C read. The 7-bit device ID is automatically shifted up by one bit to make room for the read/write bit. Returns the data from the location specified.
- BYTE	Device_ID
7-bit Device Address ID
- UINT	Address
- BYTE	AddressByteCount
Specifies the number of address bytes, Range: 1 or 2
- BYTE	Return

	Transaction_Read
Attempt to read Length number of bytes from the I2C slave to the given Buffer. Ensure that the Buffer is large enough. Returns number of bytes read, caller should check that this matches requested Length
- BYTE	Buffer
Buffer to store the incoming byte data
- UINT	Length
Number of bytes to read
- UINT	Return

	Start
Outputs a start condition onto the I²C bus.
- VOID	Return

	Transaction_Initialise
Initialise the I2C interface to communicate with a Slave device at Address Returns 0 on fail, 1 on success
- BYTE	Address
7-bit I2C Address without the shift for the R/W bit
- BYTE	Return

	Initialise
Enables the I²C hardware and performs some initialization. Should be called at the start of the program or at least before any of the other I²C functions are called.
- VOID	Return

	Initialise
Required to be used whenever the Bluetooth component is used in a program. Initialises the Bluetooth component ready for use.
- VOID	Return

Property reference

	Properties
	Channel
Channel selection
	Baud Select
Baud rate option selector
	Baud Rate
Baud rate to be used
	Stop Delay
On older microcontroller devices there is a potential for the I2C hardware channel to lock up if there is not a 10ms delay between an I2C stop event and the next I2C start event. Most modern microcontrollers will not have a problem so this property can be disabled to speed up the I2C communications.
	Slew Rate Control
Slew Rate Control Enabled or Disabled
	SMBus Inputs
When Enabled input logic thresholds are compliant with SMBus specification
	Connections
	SDA
Pin used for SDA (data signal)
	SCL
Pin used for SCL (clock signal)
	Simulations
	Label
Label shown on the comms flasher on the simulation panel.
	Scope Traces
Selects if the scope traces are automatically generated or not
	Console Data
Selects if the console data is automatically generated or not
	API