KISS Decoding example
This is not how everyone should do this, just how I setup to decode any protocol, known or not.
Some scope settings may have been changed in this series of screenshots but none that matter to the end result.
Down to business:
SPI without a CS signalSiglent STB-3 signal test board.
First we must find the Clock and obtain rock solid triggering where in this screenshot that is Stopped to show how a packet is incorrectly triggered due to no use of Holdoff to inhibit retriggering within the same packet.
We can see a packet width is ~1 horizontal div where a Holdoff setting of 200us will prevent triggering until the packet has finished.
Also at this point we can see the Clock signal is Idle High/Active Low in relation to Ch4 0V vertical position and therefore also make the trigger Edge change to Falling to correctly trigger on the first edge of the packet.
Now we can add the channel containing the data after acquiring rock solid stable triggering and start configuring Decode settings. Simple thus far.....
A little jump ahead.....
We can see above where the H Pos is set to mid display where if we magnify the timebase to closely inspect a packet part of it will be off the display and we will need to adjust H Position to see it all.
For this we have another setting that can help especially if we are to adjust the timebase so to not have the H Position we have set dance all over the display, so we lock it in a fixed position from Utility/System Settings/Reference Pos.
Now we have the settings fixed in stone it's time to configure the CS options to decode without a Clock Sense signal.
Active High and Active Low are for when you have a CS signal and in its absence we use a CLK Timeout however we need tell Decode which signal it applies to, in this case Ch4, the Clock signal.
We can use Cursors to determine the timeout required which would normally be just the length of a CS signal, the length of a packet.
In most cases CLK Timeout settings are quite forgiving if we have most other settings correct.
This guidance will get most on the right track to where they can start transferring Decode settings to the Trigger and defining an exact bit to trigger on.
If here and not getting results that make sense, be sure to check Decode Threshold settings are within the waveform amplitude levels, somewhere ~50% is usually just fine.
Have fun.
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