What is in Register 15? Why is bit 0 of Register 15 always 0? What happens when you load a value…

  
What is in Register 15? Why is bit 0 of Register 15 always 0? What happens when you load a value into Register 15 with bit 0 set? What is the initial value in R15 after a reset? What is the initial value in R14 after a reset?