[phenixbb] fixing backbone of selected part during phenix.refine

Hi, Does PHENIX can keep fix the backbone of a selected part in one chain during refinement using phenix.refine? If yes, can someone tell me the command line promt. I want to fix the backbone(N, CA, C, O) of a long helix ( 62 to 157 of chain A and also of chain B) during refinement. I have two similar helices in chain A and chain B. I am also using NCS. Thank you in advance Raja