Instruction Set Architecture—IP2022 User’s Manual 82 www.ubicom.com When  a  return  instruction  is  executed  the  subroutine  stack  is
popped,  as  shown  in  Figure  3-13.  Specifically,  the  contents  of
Stack 1 are copied into the program counter and the contents of
each stack level are moved to the next higher level. When a value
is popped off the stack, the bottom entry is initialized to 0xFFFF.
For example, Stack 1 receives the contents of Stack 2, etc., until
Stack 15 is overwritten with the contents of Stack 16. Stack 16 is
initialized to 0xFFFF.