In this note we report the first observation of salient features of the Si(111)7 x 7 reconstructed surface across monatomic steps by dynamic atomic force microscopy (AFM) in ultrahigh vacuum (UHV). Simultaneous measurements of the resonance frequency shift Delta f of the Si-cantilever and of the mean tunneling current <(I)over bar (t)> from the cleaned Si tip indicate a restricted range for stable imaging with true atomic resolution. The corresponding characteristics vs. distance reveal why feedback control via AS is problematic, whereas it is as successful as in conventional STM via <(I)over bar (t)>.