The I2C(pronounced I square Cee) is a simple communication standard intended to move small amounts of data a few inches between chips. Please See I2C Wikipedia page for additional information.
Note that I2C addresses are 7 bit. The last bit, which is not part of the address, indicates whether this is a read or write operation. So "0001 000x" is 0x8, not 0x10.
You have to be careful about selecting the power source for additional I2C devices. It is a temptation to use TP1702 which provides a spare power regulator. But keep in mind that it is steered by i2c. So under bad conditions things like internal esd protection diodes
of the added hardware pull down the I2C lines so that
the system cannot communicate with the power regulator and cannot power things on (including the additional I2C device) but also backlight, etc. The Freerunner will not boot.
On the Neo1973, we currently use the following addresses on the I2C bus:
Device | I2C address |
PCF50606 | 0001 000x |
WM8753L | 0011 010x |
LM4857 | 1111 100x |
From: Andy Green <andy@openmoko.com> To: openmoko-devel <openmoko-devel@lists.openmoko.org> Date: Wed, 02 Jul 2008 09:11:03 +0100
If you pop the top facia, I2C is available from two testpoints near the debug connector. GND is not on a testpoint there but the mounting holes at the bottom and you can grab it from a capacitor under the battery on the right of the picture too.
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