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