Be that as it may, however, "copy the settings to the trigger" does not make too much sense, IMHO. Even if I couldn't see the edge I want to trigger on beforehand, I'd still know the two digital logic levels, and can choose the trigger level from that. And then of course you're right saying that some glitches may necessitate tweaking the trigger level a bit. But this is also why I prefer to choose levels independently: In order to find some rogue glitches I'd need exactly such a threshold as I avoided to use for the decoder, to avoid upsetting it by the same glitches.
We are talking about
serial triggers here, not a simple edge trigger. Of course you can use edge/pulse/timeout triggers, maybe in conjunction with holdoff, to get a stable capture of the serial data stream, but then you get all packets, even though you might only be interested in very specific ones, e.g. with certain addresses and/or certain characters in the payload.
For this to work, the serial triggers need to be able to decode the data stream, hence also need the correct settings. There is no “trigger level” for serial triggers, just signal assignments to the input channels, separate threshold levels for each channel, polarity, idle level, baud rate, command bit inclusion and the like. On the other hand, if you turn the trigger level knob, nothing will happen at all.
There can be different concepts. Siglent uses the most obvious one: triggers and decoders are completely independent modules. Triggers are implemented in hardware, because of the speed requirements, whereas decoding is done in software because of the flexibility. Of course, we could just have one single setting that is used by both modules, but where to place them?
Some people don’t care for serial trigger and just want to see every single packet – and use some edge/pulse/timeout trigger for that. They want to find the protocol settings in the serial decoder of course.
Some other people don’t need to decode anything, they just want to trigger on a specific serial packet and watch the related signals at that point in time. These folks only need to set up the trigger and of course expect to be able to do this in the trigger settings. Btw, there have been times (long ago) where serial triggers have been free, whereas serial decoders were paid options. At about 2017, Siglent were the first to provide basic triggers and decoders (UART, SPI, I2C, CAN, LIN) for free…
Back to topic: We could have different places for accessing the serial settings and still use a common data set for them. Then any change in the decoder would immediately affect the trigger as well – and vice versa. Most of the time, this would be the wanted behavior, But since trigger and decoders can be used independently, even on different serial buses at the same time, we don’t want to limit the user (user shall be master and not slave of the machine) and consequently allow individual settings for the individual modules.
With the possibility to copy the decoder settings into the trigger as well as the trigger settings into the decoder just with a single touch, we have the best of both worlds.
Apart from trying out I have never used that copying function. In addition to making limited sense (as I wrote above), I'm also far faster just rotating the trigger level knob versus clicking through menus to reach that copying function.
I hope that you’ve realized by now that there is no “trigger level” for serial triggers and the trigger level knob has no function at all. But you can save the hassle to retype a bunch of settings. Imagine SPI as a popular example:
4 different Signals -> 4 different channels, 4 threshold levels, clock phase and CS type -> 10 settings.
That’s much more hassle than just remembering a single threshold level and then turning a knob.
There is no internal/external switch – don’t know where this error in the manual comes from, since to the best of my knowledge it has never worked any different to what it does now.
I beg to differ. I have a fairly clear memory of having played with that menu entry. Maybe you never used it because you found out early what you're describing here?
Yes, I found it out immediately – and quite honestly, this is something I set once in my lifetime and then forget about it – as long as I don’t need to do a demonstration like in my last post, but this has been the first time in my long career as Siglent DSO power user….