====== About ====== This topic covers how to connect I2C device to Carambola. For this tutorial I will use [[http://www.ti.com/product/pcf8575|PCF8575 16 bit I/O expander]]. {{:cimg1339_.jpg?direct&500|}} ====== Schematics ====== In order to connect I2C device I will need few passive components. See attached schematics. {{:carambola_i2c.png?direct&500|}} There is also power selection jumper (5V or 3.3V) and SPI pin header. Discard these for this subject. ====== Preparing Carambola ====== * run ''make menuconfig'' and select these packages: Kernel modules I2C support kmod-i2c-gpio Utilities i2c-tools package * Type ''make'' and rebuild firmware * Reflash * If you are unfamiliar with these steps read [[carambola_where_to_start|Where to start]] ====== Testing ====== Connect to Carambola with fresh firmware and type ''i2cdetect -y 0''. You should see something like: root@OpenWrt:/# i2cdetect -y 0 0 1 2 3 4 5 6 7 8 9 a b c d e f 00: -- -- -- -- -- -- -- -- -- -- -- -- -- 10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 20: 20 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 70: -- -- -- -- -- -- -- -- ====== Read data ====== root@OpenWrt:/# i2cget -y 0 0x20 0x00 w 0xffff ====== Write data ====== root@OpenWrt:/# i2cset -y 0 0x20 0x00 0xff ====== Issues ====== These utilities were written to work with I2C memory devices and lack of full I2C support. Biggest issue - it is possible only communicate with devices that have 2 bytes in I2C protocol. Although I2C on hardware level supports up to 7 (I am not exactly sure right now) bytes for both directions.