what different in SDK13 between ble_nus.c and ble_nus_c.c ?

[Mikhail]

I need use NUS services (UART over BLE) What file and functions should I use?

[endnode]

Do you have clear understanding what will be both sides of your NUS link and what GAP&GATT properties they support? Also consequences on power consumption and co-existence and interworking with other Profiles and Services (if any of these devices is multiapplicational)?

[Mikhail]

Thanks. I understand that if I want to use a central role, no need to add any characteristics to NUS service. Yes?

[endnode]

Yes. I would highly recommend to take two nRF5x boards and run NUS on both sides (ble_nus and ble_nus_c), test how it works and see where the Tx/Rx data flow (= point you will probably customize).