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AC Ripple Seen On RS-232 Serial Line
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AC Ripple Seen On RS-232 Serial Line

by earnestblimp on Sat Sep 04, 2010 2:33 pm

Hi,
I am looking at an RS-232 circuit, watching the data lines with a scope, and I switched to AC coupling to see if I could see any ripple or anything out of the ordinary. It looks clean most of the time, but I noticed that when I see DC voltage changes due to digital serial transmission, there is an associated AC voltage of about 15 volts, but just for the duration of the voltage state changes. That seems really high to me, but I didn't know if some amount of AC ripple just during the DC voltage going from 0 to 5v was ok, as long as it wasn't always on the line. Is this correct? Or am I seeing something that needs to be addressed? Should I ever see any AC ripple on a serial line? Thanks!

earnestblimp
 
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Re: AC Ripple Seen On RS-232 Serial Line

by oPossum on Sat Sep 04, 2010 2:36 pm

While the RS-232 line changes state it is no longer DC. What you are seeing is normal.

Most RS-232 transceivers output +/- 9V with no load, a bit less with load, so seeing 15V on transition is also normal.
I am the Possum, and I approve of this message. Sent from MacBook Wheel Sorry for my bad German.
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Re: AC Ripple Seen On RS-232 Serial Line

by earnestblimp on Sun Sep 05, 2010 12:26 pm

Great, thanks!

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Posts: 19
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Please be positive and constructive with your questions and comments.