Not really enough info to go on; you do not define anything about the serial method / speed or what generates it.
You can use the hardware Usart if its a standard speed and protocol.
You could just use a port to monitor for the signal and test when it changes / combine with the interrupt functions from port B if its possible to use them as inputs at all ?
Sorry, but cannot quiet grasp what you are doing with the 8 bit signal and where it comes from ?
You say need to design a signal generator ? -that produces 8 bits ? - the same or constantly changing ?
A simple way would be a shift register where you set up the 8 bits by switches and then flush them out serially to the pic.
You then want to serially read in this signal and display it a 8 bits on Port B of a Pic ?