IP2022 User’s Manual—Instruction Set Architecture www.ubicom.com 197 Example: org    0 ;set address to 0x000 ...                          ;ISR code goes here
reti  #0x4  ;return from interrupt This is an example of an interrupt service routine.
When an interrupt occurs, the CPU registers are
saved   into   a   set   of   shadow   registers.   The
program   then   jumps   to   the   interrupt   service
routine, which starts at a default address of 0x000
(software can change this address by loading a
new   interrupt   vector   into   the   INTVECH   and
INTVECL   register   pair).   The   interrupt   service
routine   should   determine   the   cause   of   the
interrupt, clear the interrupt flag bit for the event
that  raised  the  interrupt,  perform  any  required
service  for  that  event,  and  end  with  the  reti
instruction. The reti instruction restores the contents of the
program counter from the shadow registers. This
causes the IP2022 to continue program execution
from   the   point   at   which   the   program   was
interrupted. In this example, the immediate operand specifies
restoration   of   the  pre-interrupt  speed,   but  no
modification is made to the interrupt vector or the
T0TMR register.