User manual

Terminations and Bias
A transmission line should be terminated at the receiving end in its characteristic impedance. Installing a
jumper at the location labeled TRMO applies a 120Ω load in series with a 0.01μF capacitor across the
output for RS422 mode and across the transmit/receive output/input for RS485 operation. A jumper at
the TRMI location applies a load on RS422 inputs.
120
TERMOUT
0.01 F
620
620
100 pF
100 pF
+5 VDC
GND
TRx+
TRx-
:
120
TERMOUT TERMIN
120
0.01 F 0.01 F
620
620
100 pF
100 pF
100 p
F
100 p
F
+5 VDC
GN
D
Tx+
Rx+
Tx- Rx-
::
Two Wire Four-Wire
Figure 3-2: Simplified Schematic - Two-Wire and Four-Wire Connection
Full or Half-Duplex
Full-Duplex allows simultaneous bi-directional communications. Half-Duplex allows bi-directional
transmit and receiver communication but only one at a time, and is required for RS485 communications.
Proper selection depends on the wire connections used to connect the two serial ports. The following
table shows how two serial communication boards would be interconnected for the various modes. Tx
designates the transmit wires and Rx designates the receive wires.
Manual 104-ICOM-2S, 104-COM-2S 14