Nidec Digitax ST Indexer, User Manual, Page: 17 / 132

SM-Applications Modules & Motion Processors User Guide
17
Issue Number: 4
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3.6 CTNet Network Termination
It is very important in high-speed communications networks that the network
communications cable is fitted with the specified termination resistor network at each
end of the cable. This prevents signals from being reflected back down the cable and
causing interference.
The termination resistance should match as closely as possible the impedance of the
cable. For the recommended Control Techniques green CTNet cable, an 82

0.25 W
termination resistor should be fitted across the CTNet+ and CTNet- data lines at BOTH
ends of the cable run.
Figure 3-4 CTNet Network Termination
3.6.1 CTNet Cable Screen Connections
The cable shields should be linked together at the point where they emerge from the
cable, and formed into a short pigtail to be connected to CTNet shield connection on the
terminal block, as already shown.
For safety, the CTNet shield must be connected to earth at one point. This earth
connection is to prevent the cable screen from becoming live in the event of
catastrophic failure of another device on the CTNet network or along the cable run.
3.6.2 Maximum Network Length and Number of Nodes
The maximum number of nodes that can be connected to a single CTNet network is
255, however a network may need to be split into segments, separated by repeaters.
The maximum length of network cable for a CTNet network is dependent on the baud
rate and number of nodes...Refer to CTNet user guide.
Failure to terminate a network correctly can seriously affect the operation of the network.
If the correct termination resistors are not fitted, the noise immunity of the network is
greatly reduced.
WARNING
If too many termination resistors are fitted on a CTNet network, the network will be over-
loaded, resulting in reduced signal levels. This may cause nodes to miss some bits of
information, resulting in transmission errors being reported. If network overload is
excessive, the signal levels may be so low that nodes cannot detect any network
activity at all.
NOTE