A possibly dumb Q on digital oscilloscopes

[nctnico]

Technically: RS485 is (like RS232, RS422, etc, etc) only an electrical interface specification so you can run any kind of bit pattern over it which forms a communication layer.

However, if there is a UART signal over any of these kind of links you should be able to decode it using the UART decoder. It is a matter of setting the right threshold and polarity (and the regular UART parameters ofcourse).

[peter-h]

What is the difference between UART and RS232? You can set a threshold for either mode.

I know what you mean about interface versus protocol etc and I have run e.g. Manchester using RS485 chips, but normally RS422/485 is just a differential version of RS232. The data encoding is the same i.e. NRZ, with a start bit, x data bits, 1 stop bit... To decode this in the correct differential way the scope would need a facility for subtracting two channels, otherwise the decoding is just like RS232.

[rsjsouza]

One thing we could not find today was decoding data on RS422/485 i.e. the difference between two signals. There is one option called RS232, and one called UART which I assume is the TTL level at a microcontroller i.e. inverted version of RS232.

According to this datasheet, the UART is a bit more configurable.

[tggzzz]

Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...

... and to grok what isn't being said and what isn't being specified.

[rsjsouza]

Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...

... and to grok what isn't being said and what isn't being specified.

Good one!

[peter-h]

Many thanks, rsjsouza. There is way more functionality in this than I had realised, or saw in the config pages.

[peter-h]

Does the WS3034 have the capability to look at e.g. RS422 the correct way i.e. decode the two signals differentially?

[Hydron]

Can you use a maths function to find the difference between the two signals, then run the decode on that result?

[borjam]

Can you use a maths function to find the difference between the two signals, then run the decode on that result?

I would guess it's possible to use "MATH" as a source on a LeCroy. I was surprised by the ancient 9400 and how it allows you to stack operations using "MATH" as a source.

That said, in order to debug RS422/RS485 I think that a differential probe is almost mandatory. Especially with long cable runs. Common mode voltages can be a problem otherwise.

I use a Hameg HZ109 myself. You don't need a lot of bandwitdh.