> b) Another talks about HARDWARE Multi-Master IIC, but seems that this is only
> possible with 16C62 or greater or 16C73 or greater but not with a 18 pins PIC.
>
>   So if I want to use a PIC like an slave peripheric: How can I do?, I must
 use
> a great PIC?.

In order to work as a slave on an I2C bus, it must respond to each clock
pulse within a few microseconds (I don't have the specs handy, but I think
the limit's about 1us for fast devices or 5us for slow ones) by either:

[1] Reading the data or outputting data as needed
  or
[2] Ignoring the data if the device knows it's not needed
  or
[3] Asserting the clock wire until the device has done [1] or [2] (the max
    allowable time here is about 1ms I think).

Unless a PIC is doing NOTHING BUT looking at the I2C clock wire, there is
no practical way to respond in time to click edges.  Maybe something really
simple could be handled with clock-wire checks written into the code every
few instructions but I2C slave mode without hardware assist WILL be a MAJOR
CPU hog.

Some simple gates or a PLD may be offered to mitigate the CPU demands.  For
a straight slave application, the device should handle two features of the
protocol:

[1] If the device sees a falling edge on the data line while the clock wire
    is high, it should "turn itself on" (its on/off state should be readable
    by the CPU).

[2] If the device is on, it should latch the clock line low on every falling
    clock edge (and let the CPU know it's done so); the CPU should then be
    able to either clear the latch (in which case the device will latch the
    next falling edge) or turn the device off (in case the CPU can tell the
    data being transferred is not for it).

Note that with hardware rigged to do the above, a PIC should be able to easily
handle the damands of I2C.  Note two things, however:

[1] Unless the PIC responds very quickly to data which is being sent over the
    bus, it will slow down all I2C communications on the bus (even those
    data transfers which are not addressed to it).

[2] Use of hardware to perform I2C functions may require payment of royalties
    to Phillips.