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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

byte:

  S Addr7 Rd/Wr ....

becomes

  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.