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I2C: Inter-Integrated Circuit


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99-i2c.rules /etc/udev/rules.d SUBSYSTEM=="i2c-dev", MODE="0666"

I2C Primer

TWI is the same thing. SMBus is a stricter subset used in PCs: Power management, fan control, sensing battery level, and so forth. Multi-master serial bus: one or more mastercontroller devices, one or more slaveperipheral devices. 7-bit address space (112 node limit), 16 reserved addresses (10bit address space (1008 node limit) exist too) arbitrary bus speeds (0hz to 5Mhz), common speeds: 10Kbps, 100Kbps, 400Kbps. Practical distances of a few meters. Bi-directional, open drain bus. - requires external pull-up resistors. Two wires, SCL (clock) and SDA (data)

Controller always controls SCL. Start Condition - SDA falls while SCL is high. Stop Condition - SDA rises while SCL is high. Between Start and Stop, the bus is Busy. SDA Bits are sampled when SCL is high.

First 9 bits are peripheral address + R/W bit + ACK bit. Next 9 bits are data + ACK bit. Repeat until STOP condition.

I2C Lab