Manual 26166V1 MicroNet Simplex & MicroNet Plus
Woodward 83
Table 7-4. Module Specification
Ports 1 and 2: RS-232 @ 110–38.4 kBd
Ports 3 and 4: RS-232, RS-422, and RS-485 (software selectable) @ 110–57.6 kBd
Software Support: Modbus RTU
Modbus ASCII
Woodward-specific service interface
7.6.2—Installation
Termination
For RS-422, termination should be located at the receiver when one or more transmitters are connected
to a single receiver. When a single transmitter is connected to one or more receivers, termination should
be at the receiver farthest from the transmitter. Figure 7-21 is an example.
Figure 7-12. RS-422 Terminator Locations
For RS-485, termination should be at each end of the cable. If termination can't be located at the end of a
cable, put it as close as possible to the ends. Figure
5-17 is an example.
Figure 7-13. RS-485 Terminator Locations
Termination is accomplished using a three-resistor voltage divider between a positive voltage and ground.
The impedance of the resistor network should be equal to the characteristic impedance of the cable. This
is usually about 100 to 120 Ω. The purpose is to maintain a voltage level between the two differential lines
so that the receiver will be in a stable condition. The differential voltage can range between 0.2 and 6 V;
the maximum voltage between either receiver input and circuit ground must be less than 10 V. There is
one termination resistor network for each port located on the SIO board. Connection to this resistor
network is made through the 9-pin connectors on pins 6 and 9. See Figure 7-23 for termination and cable
connection examples.
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