(Note: PTZ camera must be Pelco D supported) There is a 15 pin connection port at the back of 4Ch DVR standalone. Pin 10 is for RS485-B (negative) connectionn. Pin 11 is for RS485-A (positive) connection. (Note: PTZ camera must be Pelco D supported) There is a 25 pin connection port at the back of 16/ 8Ch DVR standalone. Pin 24 is for RS485-B (negative) connectionn. Pin 12 is for RS485-A (positive) connection.