Author Topic: MSO5074 serial decoder possible bug?  (Read 382 times)

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Offline diegogmx

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MSO5074 serial decoder possible bug?
« on: March 17, 2019, 03:03:59 pm »
Either i'm completely confused about the polarity settings of the rs232 decoder or the scope has it backwards



i know this is pretty basic, but this is too basic for a bug, maybe i'm interpreting something wrong?
 

Online ataradov

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Re: MSO5074 serial decoder possible bug?
« Reply #1 on: March 17, 2019, 03:36:17 pm »
This is a correct polarity for RS-232, but not for UART. But the protocol name says RS-232, so it is ok.

I don't think that polarity icon should be read literally. This one just means "positive" in a sense "not inverted" compared to the normal for the protocol.
Alex
 

Offline diegogmx

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Re: MSO5074 serial decoder possible bug?
« Reply #2 on: March 17, 2019, 03:50:27 pm »
i think i figured it out, the logic is still inverted, however the idle state does change, so the detection of the start bit changes
 

Online ataradov

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Re: MSO5074 serial decoder possible bug?
« Reply #3 on: March 17, 2019, 03:56:10 pm »
What logic is inverted?  The idle state for RS-232 is -3 V to -25 V (often -12 V is used). So this decoding is correct for non-inverted (as configured) polarity.
Alex
 

Offline diegogmx

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Re: MSO5074 serial decoder possible bug?
« Reply #4 on: March 17, 2019, 04:09:36 pm »
you set the threshold in this case, it's not the standard rs232 (it should say uart rather than rs232), in this case it was set at about 2v
 

Offline NoisyBoy

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Re: MSO5074 serial decoder possible bug?
« Reply #5 on: March 19, 2019, 07:51:04 am »
I was just reading the user's manual today and came across this topic on page 11-9, apparently the polarity icon is "negative" in Rigol's interpretation.  I would agree the icon is somewhat confusing and backward. 


This is a correct polarity for RS-232, but not for UART. But the protocol name says RS-232, so it is ok.

I don't think that polarity icon should be read literally. This one just means "positive" in a sense "not inverted" compared to the normal for the protocol.
 

Online ataradov

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Re: MSO5074 serial decoder possible bug?
« Reply #6 on: March 19, 2019, 08:25:09 am »
The polarity icon is correct for the protocol. RS-232 looks exactly as shown on the icon.  It would be better if they just wrote "inverted" and "non-inverted".
Alex
 

Offline NoisyBoy

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Re: MSO5074 serial decoder possible bug?
« Reply #7 on: March 19, 2019, 12:45:04 pm »
X2

The polarity icon is correct for the protocol. RS-232 looks exactly as shown on the icon.  It would be better if they just wrote "inverted" and "non-inverted".
 


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