hi,everybody,I'm using keil7.20,uvision3.and I have an ok project.but when I added _push_(DPH); _pop_(DPH); to my main() func, an err always ocurrs: Build target 'Target 1' linking... *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: __POP_ MODULE: Main.obj (MAIN) Program Size: data=98.0 xdata=0 code=1730 creating hex file from "reset"... "reset" - 0 Error(s), 1 Warning(s). if move away _pop_(DPH);and everything will be ok;so I'm really confused. I think the to use _push_(); and _pop_(); are same. But what's going on with this? waiting for your help and answers.