i2c

Talks to an I2C device that has no node of its own. Each message that arrives does one transfer.

Properties

• I2C bus — the bus the device is wired to. See I2C buses.
• operation — read, write or scan.
• address — the device's address, such as 0x29. Not used by scan.
• register — the register to read or write, such as 0x80. Leave empty for a device without registers.
• length — for read, how many bytes.

Hex (0x29) and decimal (41) both work.

Output

• read — msg.payload is the bytes read.
• write — writes msg.payload and passes the message on unchanged. The payload can be bytes, a list of numbers 0–255, or one number.
• scan — msg.payload is the list of addresses that answer.

Other message fields are kept.

Behavior

If a transfer fails, the node sends nothing and its status dot says why: disconnected when nothing answers, error when the payload can't be written. The next message tries again.

Example

Read a TCS34725 colour sensor's ID register: address 0x29, register 0x92, length 1. An inject into this node, into debug, prints b'D' (0x44).