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Products => Test Equipment => Topic started by: diegogmx on March 17, 2019, 04:03:59 am

Title: MSO5074 serial decoder possible bug?
Post by: diegogmx on March 17, 2019, 04:03:59 am
Either i'm completely confused about the polarity settings of the rs232 decoder or the scope has it backwards

(https://i.imgur.com/YMjITgH.jpg)

i know this is pretty basic, but this is too basic for a bug, maybe i'm interpreting something wrong?
Title: Re: MSO5074 serial decoder possible bug?
Post by: ataradov on March 17, 2019, 04:36:17 am
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.
Title: Re: MSO5074 serial decoder possible bug?
Post by: diegogmx on March 17, 2019, 04:50:27 am
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
Title: Re: MSO5074 serial decoder possible bug?
Post by: ataradov on March 17, 2019, 04:56:10 am
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.
Title: Re: MSO5074 serial decoder possible bug?
Post by: diegogmx on March 17, 2019, 05:09:36 am
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
Title: Re: MSO5074 serial decoder possible bug?
Post by: NoisyBoy on March 18, 2019, 08:51:04 pm
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.
Title: Re: MSO5074 serial decoder possible bug?
Post by: ataradov on March 18, 2019, 09:25:09 pm
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".
Title: Re: MSO5074 serial decoder possible bug?
Post by: NoisyBoy on March 19, 2019, 01:45:04 am
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".