when I used simulator in keil5 for NRF51 software debug, there is a problem : *** error 65: access violation at 0xFFFFFFF4 : no 'write' permission. When I used the keil5 command "Map 0xFFFF0000,0xFFFFFFFF READ WRITE", the error disappeared. But, the "PC(Program Counter)" was always in 0x00000000 and the software was not running at all. Can you help me? Thank you so much.