Electronics > Beginners
Multiple receivers on a differential line
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FrankT:
I'm wiring up a quadrature rotary encoder with differential outputs to the spindle of my mill drill.
I'm running a 1 meter shielded twisted pair from the encoder to my speed controller. The encoder outputs using a uA9638C differential line driver, and the speed controller receives using a uA9637C differential line receiver, with a 100 ohm termination resistor.
What I need to do now is add an additional connection to my rotary table controller, so I can synchronise the motion between the rotary table and spindle. This cable will only be connected when the rotary table is used.
What do I need to do with the termination resistor? The datasheet seems to imply I should only have one termination resistor in the circuit. Is it ok to just have it in the first receiver and not on the 2nd one 2 meters away?
Ian.M:
Depending on the speed of the signals and the rate the speed controller samples them, you may get away with an unterminated 2m stub contributing reflections, however if you want to be certain, put a termination resistor in the rotary table and also in a dummy plug so you can properly terminate it when the rotary table isn't in use. or make the termination resistor in any device with a daisychain connector switchable.
FrankT:
Thanks. The dummy plug is a great idea. I just finished 3d printing a cap to cover the socket, so a dummy plug will be even better.
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