Two-Wire Interface

Two-Wire Interface for Arduino – Asynchronous and Synchronous Transactions – Controller and Target modes.

• Asynchronous (non-blocking) transactions using the Two-Wire Interface (TWI) interrupt service routine.
• Synchronous (blocking) transactions by polling the TWI interrupt flag.
• Supports target devices with an internal address register of 1, 2, or 3 bytes.
• 32 ms timeout provided by the Watchdog Timer.
• Buffers are supplied by the caller.
• Transaction limit of 65535 bytes.
• Internal pullup resistors on SCL and SDA are disabled by default.

Asynchronous transactions (default)

These functions return an enum to indicate the status of the transaction. If it fails to start, it returns TWI::Results::FailedToStart. If it started, it returns TWI::Results::Started.

To find out whether the transaction completed successfully, call twi.GetResult() or twi.IsSuccess() in loop().

Read buffer

twi.Read(target_address, rx_buffer, rx_buffer_size);

Read buffer from internal address

twi.Read(target_address, internal_address, internal_address_size, rx_buffer, rx_buffer_size)

Write buffer

twi.Write(target_address, tx_buffer, tx_buffer_size);

Write buffer to internal address

twi.Write(target_address, internal_address, internal_address_size, tx_buffer, tx_buffer_size);

Write byte

twi.Write(target_address, data_byte);

Write byte to internal address

twi.Write(target_address, internal_address, internal_address_size, data_byte);

Synchronous transactions (optional)

Specify the wait flag TWI::Modes::Wait to enable synchronous mode, e.g. to read a buffer synchronously:

twi.Read(target_address, rx_buffer, rx_buffer_size, TWI::Modes::Wait);

These functions return an enum to indicate the status of the transaction. If it fails to start, it returns TWI::Results::FailedToStart. If it completes successfully, it returns TWI::Results::Success.

Internal address register

Some target devices have addressable internal registers for configuration and control information. The internal address size can be 1, 2 or 3 bytes:

Size of internal address register (bytes)	Internal address range
1	0 to 255
2	0 to 65,535
3	0 to 16,777,215

Timeouts

There is a 32 ms timeout provided by the Watchdog Timer to detect when the I²C bus freezes. When triggered, the TWI will be reset.

Buffers

The caller supplies the buffer and the buffer size. This provides greater flexibility, e.g. a display can be double buffered using asynchronous transactions where the second buffer can be populated with data in loop() while the first buffer is being sent to the display by the TWI ISR.

Internal pullup resistors

The internal pullup resistors on SCL and SDA are disabled by default. To enable them, call twi.Enable(twi_frequency, pullups) with the second parameter set to true.

Example

This simulator example demonstrates how to communicate with a Motion Processor Unit – the MPU-6050 – on the I²C bus. It also demonstrates recovery from a communication error, i.e. press the buttons to freeze the I²C bus, whence upon releasing them, the TWI resets and continues with normal communication: TWI MPU-6050 Test: