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How can a 2-channel DSO "trigger and decode" the 4 signal SPI protocol?
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sja:
I see that some 2 channel DSO offer as standard 'Serial bus triggering and decoding' including SPI. For example the Siglent SDS1202X-E.

But SPI has 4 lines: CLK, CS, MISO and MOSI.

So my question is: how can a 2 channel DSO decode the 4 signal SPI?

I guess that you would hook the DSO to the MISO and MOSI buses and the DSO would then deduce the clock speed automatically and decode *all* signals on the MISO/MOSI buses. Is that how they do it?
rvalente:
Easy...

never mind about CS and CLOCK in the trigger channel, I'm pretty sure the Keysight 1052a works this way
pcprogrammer:
Just look at the data stream important to you. So connect CLK and MISO or CLK and MOSI to see what is on the bus.

I don't think it is really possible to decode without the clock and determining the clock from the data signal can be very hard since there is no start or stop bit to go on. So it would need to know the frequency of the clock to be able to make up its own clock by syncing it to an edge on a data line.
sja:
Thanks for the replies.

I have a looked again at the Siglent SDS1000X manual and it does seem to be in line with what pcprogrammer suggests. Though I do find the manual to be not very clear at all.

Has anyone ever used the SPI decode feature on a 2 channel DSO?

tautech:

--- Quote from: sja on October 19, 2022, 03:13:58 pm ---Thanks for the replies.

I have a looked again at the Siglent SDS1000X manual and it does seem to be in line with what pcprogrammer suggests. Though I do find the manual to be not very clear at all.

Has anyone ever used the SPI decode feature on a 2 channel DSO?

--- End quote ---
With the 2ch Siglents decoding on a 3 or 4 wire bus use the Clk Timeout feature, a falling edge trigger and Holdoff to prevent retriggering within a packet.

Tell me how that goes and I could post some examples later if required.
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