The 16F627 or 16F628 is a better choice over the F84. It has a
  built-in UART that can be used to address other PICs by "name",
  as it can transmit codes that will start other F628s working. It will=20
  also be easier for you to interface to the RS232 of a PC

  You can still use I2C or your own custom bit-banging if you want
  to stick with the F84 (or indeed use it with the F628). Take a look=20
  at how I2C systems work and emulate it with PICs. One advantage
  you have with the micros is that they are smarter than I2C chips
  like memories, and it would be possible to have full duplex I2C. That
  is, one portion of the PIC can be a listening slave, another portion
  can be a transmitting master. It's something that would be good
  to set out on paper and do a logic flow. With processor speeds
  of 20MHz, I2C at 400kHz means a lot of room to manouevre

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