[Fwd: Re: [U-Boot-Users] Proposal to add "ispeed" (I2C speed) command]

[Tolunay Orkun]

>> Do you think it is legal to clock the I2C bus at 400 kHz  when  there are
>> devices  on  the bus that are spec'ed only for 100 kHz? I may be wrong,
but
>> such an idea sounds awfully risky to me.
>
> Per Philips AN10216-01 I2C Manual (March 24, 2003) you can do this legally
> if you use I2C repeater such as PCA9515. This device isolates the 100kHZ
> only segment when you are talking to 400kHz segment at fast mode.

Some additional info:

The I2C-Bus Specification Version 2.1 (Jan 2000) section 13.5 says:

"13.5 Mixed speed modes on one serial bus system.

If a system has a combination of Hs-, Fast-, and/or Standard-mode devices,
it's possible, by using an interconnection bridge, to have different bit
rates between different devices (see Fig 24 and Fig 25). .... Such a
bridge can be implemented in any IC as an autonomous circuit. ..."