path: root/Documentation/i2c/ten-bit-addresses
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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/i2c/ten-bit-addresses
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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+The I2C protocol knows about two kinds of device addresses: normal 7 bit
+addresses, and an extended set of 10 bit addresses. The sets of addresses
+do not intersect: the 7 bit address 0x10 is not the same as the 10 bit
+address 0x10 (though a single device could respond to both of them). You
+select a 10 bit address by adding an extra byte after the address
+ S Addr7 Rd/Wr ....
+ S 11110 Addr10 Rd/Wr
+S is the start bit, Rd/Wr the read/write bit, and if you count the number
+of bits, you will see the there are 8 after the S bit for 7 bit addresses,
+and 16 after the S bit for 10 bit addresses.
+WARNING! The current 10 bit address support is EXPERIMENTAL. There are
+several places in the code that will cause SEVERE PROBLEMS with 10 bit
+addresses, even though there is some basic handling and hooks. Also,
+almost no supported adapter handles the 10 bit addresses correctly.
+As soon as a real 10 bit address device is spotted 'in the wild', we
+can and will add proper support. Right now, 10 bit address devices
+are defined by the I2C protocol, but we have never seen a single device
+which supports them.