AH500 Module Manual 10.3.4 Choice and Purpose of a DeviceNet Terminal Resistor Choice of a DeviceNet Terminal Resistor A DeviceNet network needs to connect a terminal resistor of 121 ohm at both ends of the trunk cable respectively. The thick cable represents the main cable and the thin cable represents the sub-cable. Purpose of a DeviceNet Terminal Resistor The terminal resistor is used for eliminating the signal reflection in the communication cable. All signal transmission cables have the characteristic impedance. The characteristic impedance of Delta DeviceNet communication cable is about 121 ohm.
When being transmitted to the end of the communication cable, because the impedance of the end is different from the characteristic impedance, the signal will be reflected, which will interfere with the new signal and the signal wave form distortion will happen. The phenomenon of the signal wave form distortion is not obvious in the short-distance transmission. But the wave form distortion will become severe with the increasing communication cable. Therefore, the two ends of the trunk cable must be installed with the terminal resistors respectively.
Installation Position of a Terminal Resistor The DeviceNet communication cable consists of five wires such as red wire, blue wire, white wire, black wire and shielded wire as below. 10-12 Product picture Type Function TAP-CB01 TAP-CB01: DeviceNet trunk cable TAP-CB02 TAP-CB02: DeviceNet drop cable