MSO5074 serial decoder possible bug?

[diegogmx]

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?

[ataradov]

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.

[diegogmx]

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

[ataradov]

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.

[diegogmx]

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

[NoisyBoy]

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.

[ataradov]

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".

[NoisyBoy]

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".