Instruction Set Architecture—IP2022 User’s Manual 78 www.ubicom.com Returning from a subroutine restores the saved program counter
contents,  which  causes  program  to  resume  execution  with  the
instruction  immediately  following  the  call  instruction  (a  nop
instruction, in the above example) A program memory address is a 16-bit word address. The jmp
and call instructions specify only the lowest thirteen bits of the
jump/call address. The upper 3 bits come from the PA2:0 bits of
the    STATUS    register.    An    indirect    relative    jump    can    be
accomplished by adding the contents of the W register to the PCL
register (i.e. an add pcl,w instruction). Program control instructions such as jmp, call, and ret alter
the normal program sequence. When one of these instructions is
executed,   the   execution   pipeline   is   automatically   cleared   of
pending instructions and refilled with new instructions, starting at
the new program address. Because the pipeline must be cleared,
three clock cycles are required for execution, one to execute the
instruction and two to reload the pipeline. call add_2bytes ;call subroutine
;add_2bytes nop ;execution returns to here
;after subroutine is finished ...
add_2bytes: ;subroutine label ... ;subroutine code goes here ret ;return from subroutine