I'm trying to start me code at 0x4000 address for debugging porpuse. I'm using uvision 2.39 C51 7.07 and i get a warning: *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?B_SWITCH0 MODULE: STARTUP.obj (?C_STARTUP) *** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL SYMBOL: ?B_SWITCH0 MODULE: STARTUP.obj (?C_STARTUP) ADDRESS: 0681H which is the problem? i have added the startup.a51 file to my project and set: CSEG AT 4000H