Electronics > Repair
Bad RS422 signal?
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Alex_Baker:
I am attempting to read RS422 data  from a Lowrance HDS9 sonar/chart plotter. It can output and recieve data through a 4-wire RS422 interface. I am having troubles reading data and decided to use an oscilloscope. The below image is what I captured by putting the scope probe on the two TX wires.

I do not have much experience with RS422, but this looks bad. Can anybody confirm this suspicion?
hexreader:
First thing to do is change oscilloscope channel 1 coupling from AC to DC

... or use channel 2, which is already DC coupled.
Alex_Baker:
Dang, I can't believe I did that.

Probing a "good" rs422 signal looked fine with channel 1 though, so I don't think that is necessarily the problem. Unfortunately I wont be able to do more testing until Monday, this equipment is at a school lab.
hexreader:
Another thing - trigger on falling edge, not rising

Good luck :)
Alex_Baker:

--- Quote from: hexreader on August 09, 2024, 09:55:08 pm ---Another thing - trigger on falling edge, not rising

Good luck :)

--- End quote ---
That would not change how the signal looks, would it? why would it matter?
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