Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Min Input
FIELDLAYER_RANGEMAP_MININParameter: Max Input
FIELDLAYER_RANGEMAP_MAXINParameter: Min Output
FIELDLAYER_RANGEMAP_MINOUTParameter: Max Output
FIELDLAYER_RANGEMAP_MAXOUT