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