[phenixbb] on the protonation state of HIS

Dear All,   There may be PDB files which shows different protonation  state of HIS, at least there is PDB file shows double protonated HIS. At which resolution of the crystal can allow us to distinguish different protonation states of HIS?   How do Phenix and Coot give different protonation states of HIS?   I am looking forward to getting your reply.   Cheers,   Dialing