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node_modules/i2c-bus/doc/raspberry-pi-software-i2c.md

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+## Configuring Software I2C on the Raspberry Pi
+
+Raspbian has a software I2C driver that can be enabled by adding the following
+line to `/boot/config.txt`:
+
+```
+dtoverlay=i2c-gpio,bus=3
+```
+
+This will create an I2C bus called `/dev/i2c-3`. SDA will be on GPIO23 and SCL
+will be on GPIO24 which are pins 16 and 18 on the GPIO header respectively.
+
+For further information about `i2c-gpio` and the parameters it supports see
+`/boot/overlays/README` on the Raspberry Pi.
+
+The advantage of software I2C over hardware I2C on the Raspberry Pi is that
+software I2C supports I2C clock stretching. Hardware I2C doesn't support I2C
+clock stretching due to a
+[hardware bug](http://www.advamation.com/knowhow/raspberrypi/rpi-i2c-bug.html).
+
+Some devices like the BNO055 9-axis absolute orientation sensor rely on I2C
+clock stretching and will not function correctly with hardware I2C on a
+Raspberry Pi. Using software I2C to communicate with the BNO055 will resolve
+this issue.
+
+Another typical use case for software I2C is communication with AVR
+microcontrollers, for example, the ATmega328P microcontroller on an Arduino
+UNO. AVR microcontrollers are not particularly fast and it's relatively easy
+to implement AVR code that relies on I2C clock stretching. Using software I2C
+to communicate with the AVR will resolve I2C clock stretching issues.
+