I am using NMOS transistors. when I do the DRC I got a message of "floating NSUNB" while as I think i should not receive like this message if the nmos has PSUB ??
Probably NWELL & NSUB are the same: a (relatively) deep (and - by this - light = n- ) nwell diffusion, in the a.m. picture called 'LVNW' (low voltage n-well) in magenta color.
The problem is that the designations are fab-specific.
What you call "N implant" probably is - in the a.m. picture - the flat-lying N+ contact implant (light magenta colored), which is always necessary for each NWELL and close to each PMOS source.