[HECnet] Disallow login on DZ line in VMS

The recent thread "Disallow system from dz lines (OpenVMS/VAX 7.3)" started me wondering how to entirely disable the login prompts on a given serial line, such as to use the port for some other purpose like controlling external hardware. I've been trying to find out how to do that in the manuals, but I haven't found it yet. It seems like it might be something to do with SET TERM, but I don't see obvious flags for that. Can anybody offer any hints? I won't be too surprised if my eyes have already glided over the answer in the manuals and HELP SET TERM text.