Depends on how much voltage the diode puts out when it's exposed to light, I'm not so sure a photo diode can be used in a voltage mode on a PIC input without amplification. If reverse biased the photo diode will act like a varactor, but again the timing precision of the PIC may or may not be good enough for your diode and doing PWM and precise timeing on 80 pins would be likley not practical, most people have trouble measuring capacitance on one pin let alone 80. I think your best bet would be any PIC (or AVR my preference) with the photo diodes connected to a simple transistor as an amplifier for the PICs I/O lines. This is one of the reasons photo transistors exist, the photodiode is coupled to a transistor in a single unit. You need to explain the precision and refresh rate you need as well as they will greatly influence the circuit you'll build.