Commit | Line | Data |
---|---|---|
ccf988b6 MCC |
1 | ===================== |
2 | I2C Ten-bit Addresses | |
3 | ===================== | |
4 | ||
89140f41 | 5 | The I2C protocol knows about two kinds of device addresses: normal 7 bit |
1da177e4 LT |
6 | addresses, and an extended set of 10 bit addresses. The sets of addresses |
7 | do not intersect: the 7 bit address 0x10 is not the same as the 10 bit | |
cbb44514 | 8 | address 0x10 (though a single device could respond to both of them). |
cfa0327b WS |
9 | To avoid ambiguity, the user sees 10 bit addresses mapped to a different |
10 | address space, namely 0xa000-0xa3ff. The leading 0xa (= 10) represents the | |
11 | 10 bit mode. This is used for creating device names in sysfs. It is also | |
12 | needed when instantiating 10 bit devices via the new_device file in sysfs. | |
1da177e4 | 13 | |
cbb44514 JD |
14 | I2C messages to and from 10-bit address devices have a different format. |
15 | See the I2C specification for the details. | |
1da177e4 | 16 | |
cbb44514 JD |
17 | The current 10 bit address support is minimal. It should work, however |
18 | you can expect some problems along the way: | |
ccf988b6 | 19 | |
cbb44514 JD |
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 | ||
31 | Note that 10-bit address devices are still pretty rare, so the limitations | |
32 | listed above could stay for a long time, maybe even forever if nobody | |
33 | needs them to be fixed. |