ten-bit-addresses.rst (1624B)
1===================== 2I2C Ten-bit Addresses 3===================== 4 5The I2C protocol knows about two kinds of device addresses: normal 7 bit 6addresses, and an extended set of 10 bit addresses. The sets of addresses 7do not intersect: the 7 bit address 0x10 is not the same as the 10 bit 8address 0x10 (though a single device could respond to both of them). 9To avoid ambiguity, the user sees 10 bit addresses mapped to a different 10address space, namely 0xa000-0xa3ff. The leading 0xa (= 10) represents the 1110 bit mode. This is used for creating device names in sysfs. It is also 12needed when instantiating 10 bit devices via the new_device file in sysfs. 13 14I2C messages to and from 10-bit address devices have a different format. 15See the I2C specification for the details. 16 17The current 10 bit address support is minimal. It should work, however 18you can expect some problems along the way: 19 20* Not all bus drivers support 10-bit addresses. Some don't because the 21 hardware doesn't support them (SMBus doesn't require 10-bit address 22 support for example), some don't because nobody bothered adding the 23 code (or it's there but not working properly.) Software implementation 24 (i2c-algo-bit) is known to work. 25* Some optional features do not support 10-bit addresses. This is the 26 case of automatic detection and instantiation of devices by their, 27 drivers, for example. 28* Many user-space packages (for example i2c-tools) lack support for 29 10-bit addresses. 30 31Note that 10-bit address devices are still pretty rare, so the limitations 32listed above could stay for a long time, maybe even forever if nobody 33needs them to be fixed.