Termination Resistor Switch

- December 19, 2018

Ive encountered some devices for which i have no schematics that have a built in toggle to enable or disable canbus termination and im wondering how this is usually achieved. The bus terminations are active and must be electrically powered.

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The resistors are rather critical in a canbus network.

Termination resistor switch. Canbus utilizes a nominal impedance of 120w which is why we use a 120w resistor on each end. The terminating resistors used on the ends of the network should match with the characteristic impedance of the wire pairs to help avoid signal reflections. Placing it at the end of the line eliminates all reflections although this approach results in higher power dissipation.

With profibus dpdp is the bus terminations are integrated in the connectors and can be activated and deactivated by a switch. This solution eliminates the need of using manual type jumpers like header pins with a shunt. However rg 6 should not be used for 10base2 which should use rg 58 as the impedance mismatch can cause phasing problems with the baseband signal.

Rs 485 termination resistor switch solution 10 introduction this document provides a solution for connecting and disconnecting the rs 485 termination resistor in multi protocol applications using a photomos relay. The most popular approach to termination is parallel termination where you place a resistor across each end of the physical link. For standard termination you would match the termination resistor value with the differential mode characteristic impedance of the cabling on both ends of the network.

This ensures the proper termination of signals traveling in both directions on the bus. This applies to the first and last node of a segment. Antenna cables are sometimes used for internet connections.

I could see them use an analog switch in series with a 120 ohms resistor but perhaps theres easiercheaper ways of doing this. A terminating resistor for a television coaxial cable is often in the form of a cap threaded to screw onto an f connector. This supply voltage for the active bus termination can be taken from the connected bus node.