I'm having a problem with normal execution of my code while ASC0 interrupt is enabled (of ST10F168) and external memory is enabled. In my small program I'm sending a character 'a' to serial port and check the same on hyperterminal if I'm able to receive it successfully. The above result is satisfactory as long as I don't have any ISR placed in my code. The moment I place an ISR, the code stops functioning. I've checked my memory map, and I am not able to think of any logical reason to get such a performance. Can anybody help me find the mistake? Thanks in advance, Regards, Sadhana.