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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 18:20:36 -0400
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 18:20:36 -0400
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/i2c/ten-bit-addresses
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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1The I2C protocol knows about two kinds of device addresses: normal 7 bit
2addresses, and an extended set of 10 bit addresses. The sets of addresses
3do not intersect: the 7 bit address 0x10 is not the same as the 10 bit
4address 0x10 (though a single device could respond to both of them). You
5select a 10 bit address by adding an extra byte after the address
6byte:
7 S Addr7 Rd/Wr ....
8becomes
9 S 11110 Addr10 Rd/Wr
10S is the start bit, Rd/Wr the read/write bit, and if you count the number
11of bits, you will see the there are 8 after the S bit for 7 bit addresses,
12and 16 after the S bit for 10 bit addresses.
13
14WARNING! The current 10 bit address support is EXPERIMENTAL. There are
15several places in the code that will cause SEVERE PROBLEMS with 10 bit
16addresses, even though there is some basic handling and hooks. Also,
17almost no supported adapter handles the 10 bit addresses correctly.
18
19As soon as a real 10 bit address device is spotted 'in the wild', we
20can and will add proper support. Right now, 10 bit address devices
21are defined by the I2C protocol, but we have never seen a single device
22which supports them.