EDIS stands for Electronic Distributorless Ignition System. It replaces the DIS system. I am not completely certain which system is in what car but I do know that starting in 96, Ford began incorporating this function into the ECU in some models. It's entirely possible that we have a modified DIS system because of our higher than average redline, but the systems are similar.
The EDIS uses engine speed and crank angles to calculate timing info. The PIP signal is sent to the ECU early so that the ECU can look up proper timing advance for engine conditions. The ECU sends the SAW signal back to the EDIS to trigger firing at the appropriate time. If no PIP or SAW signals are sent, the EDIS goes ahead and fires the coil at the latest possible time which is "base timing".
