Hi, That routine should implement couple to see or to print in the serial window, in the C09-L? Without using the timers 0 and 1... In uVision2 the linker tells me that there is an error: ERROR 103: "EXTERNAL ATTRIBUT DO NOT MATCH PUBLIC" SYMBOL: ?_PRINTF?BYTE MODULE: C: /..... /C51fpl.lib (PRINTF) CHACK