Enables communication with I2C devices. Currently only supports one I2C port per board.
Added in Firmata protocol version 2.1.0.
Updated in Firmata 2.5.1 to enable setting auto-restart by setting bit 6 of byte 3. Updated in Frimata 2.12 to enable transaction control in 7 bit mode. For boards with long error timeouts (e.g. ESP32 with recent firmware), this ensures that replies can be correctly linked to their requests.
0 START_SYSEX (0xF0)
1 I2C_REQUEST (0x76)
2 slave address (LSB)
3 slave address (MSB) + read/write and address mode bits
{bit 7: always 0}
{bit 6: auto restart transmission, 0 = stop (default), 1 = restart}
{bit 5: address mode, 1 = 10-bit mode}
{bits 4-3: read/write, 00 = write, 01 = read once, 10 = read continuously, 11 = stop reading}
{bits 2-0: slave address MSB in 10-bit mode, transaction sequence number in 7-bit mode}
4 data 0 (LSB)
5 data 0 (MSB)
6 data 1 (LSB)
7 data 1 (MSB)
...
n END_SYSEX (0xF7)
A note about read/write modes (above). The read continuously mode indicates that
the firmware should continuously read the device at the rate specified by the
sampling interval. A firmware implementation should support read continuous mode
for several I2C devices simultaneously. Sending the stop reading command will
end read continuous mode for that particular device.
auto-restart (byte 3, bit 6) is needed by some devices such as the MMA8452Q accelerometer and the MPL3115As altimeter
0 START_SYSEX (0xF0)
1 I2C_REPLY (0x77)
2 slave address (LSB)
3 slave address (MSB). Bits 0-2 return the transaction sequence from the request in 7 bit mode.
4 register (LSB)
5 register (MSB)
6 data 0 (LSB)
7 data 0 (MSB)
...
n END_SYSEX (0XF7)
0 START_SYSEX (0xF0)
1 I2C_CONFIG (0x78)
2 Delay in microseconds (LSB) [optional]
3 Delay in microseconds (MSB) [optional]
... user defined for special cases, etc
n END_SYSEX (0xF7)
The optional Delay is for I2C devices that require a delay between when the
register is written to and the data in that register can be read.