System Architecture—IP2022 User’s Manual 38 www.ubicom.com completely independent of the 16-level call/return stack used for
subroutines. The contents of the DATAH and DATAL registers are pushed to
their  shadow  registers  4  cycles  after  the  interrupt  occurs,  to
protect the result of any pending  iread instruction. Therefore,
software should not access the DATAH or DATAL registers during
the first instruction of an ISR.