| Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | The I2C protocol knows about two kinds of device addresses: normal 7 bit |
| 2 | addresses, and an extended set of 10 bit addresses. The sets of addresses |
| 3 | do not intersect: the 7 bit address 0x10 is not the same as the 10 bit |
| 4 | address 0x10 (though a single device could respond to both of them). You |
| 5 | select a 10 bit address by adding an extra byte after the address |
| 6 | byte: |
| 7 | S Addr7 Rd/Wr .... |
| 8 | becomes |
| 9 | S 11110 Addr10 Rd/Wr |
| 10 | S is the start bit, Rd/Wr the read/write bit, and if you count the number |
| 11 | of bits, you will see the there are 8 after the S bit for 7 bit addresses, |
| 12 | and 16 after the S bit for 10 bit addresses. |
| 13 | |
| 14 | WARNING! The current 10 bit address support is EXPERIMENTAL. There are |
| 15 | several places in the code that will cause SEVERE PROBLEMS with 10 bit |
| 16 | addresses, even though there is some basic handling and hooks. Also, |
| 17 | almost no supported adapter handles the 10 bit addresses correctly. |
| 18 | |
| 19 | As soon as a real 10 bit address device is spotted 'in the wild', we |
| 20 | can and will add proper support. Right now, 10 bit address devices |
| 21 | are defined by the I2C protocol, but we have never seen a single device |
| 22 | which supports them. |