Quatech QSP-200/300 - Manual (Page 44)

6.4 Termination Resistors
No termination resistors are provided on the QSP-200/300 ports. Both output and input signals
are connected only to the external connector. Any termination which is required must be added
externally.
+
-
RS-422/485 Receiver
Rt
RXD+
RXD-
+
-
RS-422/485 Receiver
Rt
AUXIN+
AUXIN-
RS-422
100 ohm 1/2W resistor RS-485
60 ohms total resistance
(120 ohms at each end)
Recommended Termination Resistor Values
Figure 7. RS-422/485 Termination
6.5 2-Wire Operation
The QSP-200/300’s ports may be configured for either full duplex or half duplex operation. By
default, the RS-422/485 ports are configured for full duplex operation with the RS-422/485
output drivers always enabled.
In half duplex mode, the RS-422/485 transmitter may be enabled and disabled via the RTS
(request to send) or DTR (data terminal ready) signals. Both RTS and DTR are controlled
through the Modem Control Register of the 16550.
QSP-200/300 User's Manual 38