4/6/2024 3:39 PM | |
Joined: 3/28/2010 Last visit: 8/21/2024 Posts: 1052 Rating:
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I'm one of the guys that knows that RS-485 low speed (9600 baud) and short runs (2m) will operate without a terminating resistor. But I still wire in a terminating resistor just so lack of termination does not become an issue if there are problems down the road. If you use any cable intended for digital communications, the cable will have a model number printed on the cable insulation and you can find the characteristic impedance on the vendor's spec sheet for that cable. There's a good video showing the effect of energy reflection creating distortion of a square wave wave form with all the conditions between an open circuit, a short circuit and the in-between conditions using with a variable resistor connected at the end of cable: the terminating resistor. https://www.youtube.com/watch?v=zrDxSM91Jcg |
Last edited by: Jen_Moderator at: 04/08/2024 07:19:51Video embedded. |
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4/8/2024 4:49 PM | |
Joined: 1/20/2022 Last visit: 8/20/2024 Posts: 368 Rating:
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what a fantastic video! looks like i might be buying a belden cable with the premium price as it has a documented impedance of 120 ohm rather than belden like cables with some random values like 80,90 etc. I can find a resistor of 120 ohm - no problem but i am not able to go to the depth of tuning a no name cable to make it square. Many thanks
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