National Instruments RS485 - Manual (Page 12)

NI 9871 Operating Instructions 12 ni.com
RS485 Transceiver Control
Refer to Table 3 for a listing of TX and RX enable conditions for
the different RS485 transceiver control modes.
NI 9871 Hardware Overview
The NI 9871 has four independent RS485/RS422 ports that are
isolated from the other modules in the system. Each port is fully
compatible with the ANSI/EIA/TIA-485 standard.
Table 3. Transceiver Control Pin Conditions
Enable 4-Wire
2-Wire
DTR/Echo DTR/No Echo Auto
TX On DTR DTR TX
RX On On DTR# TX#