Cable terminators are required on both ControlNet and DeviceNet networks to prevent reflections. This statement is true or false?

• A. True
• B. False
• C. Only ControlNet
• D. Only DeviceNet

Answer: (A)

Signals on these serial fieldbus networks travel along a shared transmission path, so the line must be terminated at each end to prevent reflections. When the far end isn’t terminated, the outgoing pulse bounces back along the cable, causing distortions, timing errors, and possible data corruption, especially on longer runs or at higher speeds.

ControlNet uses a coaxial backbone with a characteristic impedance around 75 ohms, so a 75-ohm terminator is placed at each end of the trunk to absorb energy and match the line. DeviceNet, which is CAN-based, requires 120-ohm termination at both physical ends of the trunk to keep the CAN differential signaling stable and free of reflections. Drop lines that connect devices to the trunk do not receive terminators.

Therefore, cable terminators are indeed required on both ControlNet and DeviceNet networks to prevent reflections.