Communication between controllers

Dear all i am designing a project in which i have to control three phase volatges currents and many other parameters according to the desicions. m using 4 microcontrollers one is 8051 and 3 pic 16f688. i want to make communication between these four controllers using minimum i/o s . is that possible that the 3 pic controllers communicate with 8051 using usart communication ?
or 1st pic send data to 2nd pic and then 2nd sends data of 1st and 2nd to 3rd pic and then 3rd pic transfers all the data to 8051..


which method will be easier and better and which communication is possible.i mean to say is usart better or i will have to use SPI communication in which per controller 3 pins will be accquired.

USART should be fine, but it seems a bit obscure mixing different types of controllers?.

Depending exactly what you're trying to do, passing data from one to the next is probably the easiest way?.

You could daisy chain them or perhaps wire them in a 'star' configuration using open drain drivers for master/slave operation.

The 8051 is the stickler for sure, why not use a Pic as a master? You could then use say Master I2C (two pins), with the 16f688's as slaves. Whoops, see you can't use the 16f688 as I2C slaves, never mind.

You can use the 16F88 as an I2C slave.