I linked the EPM900 to PC's RS232 port to emulate serial communication. In main function an infinite loop is written to wait for serial port IRQ. A break point is set in the start of ISR. When EPM900 received a byte of data, serial port interrupt happened, and emulation suspended because of that break point. I wanted to run the following codes in ISR by single step, but the "next statement" arrow always pointed to the infinite loop in main function. It seems that running ISR by step is not permitted by using EPM900 as emulator, doesn't it?