A few meters maximum for reliable operation, especially at 400KHz.  You can
get I2C bus extenders to drive longer lines, and there is an app-note on the
philips site somewhere of driving I2C for over 1KM.  However, I2C was never
designed for this type of operation, it was designed to connect many IC's on
a PCB to be controled by one or more micros.  e.g. televisions almost always
use I2C to control the various sections of the TV from a micro.

Mike

> -----Original Message-----
> From: ckchan [SMTP:ckchan4@PC.JARING.MY]
> Sent: Thursday, June 22, 2000 1:51 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: [PIC]: I2C for PIC-PIC communication?
>
> Greetings,
>
>
> does anybody know what is the maximum length for SDA and SCL ?? i mean,
> rs485 can
> go to 1 or 1.5 KM, what about I2C lines ?
>
>
> regards,
> ckchan
>
>
>
> "Alan B. Pearce" wrote:
>
> > The first step in using I2C is probably to go to the Philips web site,
> and get
> > the specification document. It is available as a PDF file. I found it
> without
> > much difficulty. It goes into the waveform timings, the different speed
> ranges,
> > and interfacing between different voltage families. This would be an
> essential
> > document to have if you want to try and bit bang the interface.