Question: PSoC1 has only one shield electrode on chip but PSoC3/5 supports multiple shield electrodes. What is the use for multiple shield electrodes? How to select how many shield electrodes to be used?
Answer: Multiple Shields are available in PSoC 3/5 to allow simplified routing on PCBs so that a single shield trace does not need to cross as many sensor traces possibly reducing board cost (layers) and/or improving signal to noise because of improved trace layout and ground plane coverage. One shield pin will also work just as well ignoring the mentioned layout issues. The Shields do no need to be connected together on the PCB because they are already connected together inside the device using an analog global bus. There is only 1 shield on PSoC1 because it is hard wired rather than using the flexible buses of PSoC 3/5.
