Hi, The compile error is: WARNING L15: MULTIPLE CALL TO SEGMENT SEGMENT: ?PR?_STRTONUM?PARSE CALLER1: ?PR?TC0?PERIPHERAL CALLER2: ?C_C51STARTUP The callers TC0 is an ISR using reg bank 2 and I don't know about the c51startup. The called function STRTONUM is using the directive of #pragma NOAREGS so can be called for any functions. The question is why I still got the multiple call error? Thanks for answering my question. By the way, C51 is V6.21, BL51 is V4.21 and LIB51 is V4.20. chao.