I am trying to find out how many SCI ports this board really has. I only see 2 on the pinout, but in the data sheet there are 3 more listed behind CAN3 and SPI2. However, when I try to use these SCI channels, i get no response from the interrupt, nor any output. Using the PPS/PER/WOM registers doesn't seem to have an effect. Do these really exist? How do I implement them?