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How can a 2-channel DSO "trigger and decode" the 4 signal SPI protocol?

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Fungus:

--- Quote from: sja on October 19, 2022, 12:10:06 pm ---how can a 2 channel DSO decode the 4 signal SPI?

--- End quote ---

"sub-optimally" and "with a lot of messing around"

sja:
I think the reply from Fungus sums up well what I have now understood.

JDubU:
Maybe I'm missing something, but I don't know why anyone would use a scope to decode low(ish) bitrate serial protocol streams.
Investigating why a serial interface is failing at the waveform level using a scope can be very useful, but looking for protocol encoding/decoding errors in long data streams is mostly really frustrating.

The proper tool for protocol decoding is a logic analyser like a Saleae (or similar).

Fungus:

--- Quote from: JDubU on October 21, 2022, 05:52:17 pm ---Maybe I'm missing something, but I don't know why anyone would use a scope to decode low(ish) bitrate serial protocol streams.
Investigating why a serial interface is failing at the waveform level using a scope can be very useful, but looking for protocol encoding/decoding errors in long data streams is mostly really frustrating.

The proper tool for protocol decoding is a logic analyser like a Saleae (or similar).

--- End quote ---

Correct.

A 'scope is useful for checking signal integrity and looking at small packets. After that you probably need a logic analyzer.

alm:
If you have both a scope and a logic analyzer available, and want to just look at the protocol level, then clearly a logic analyzer, or even a protocol analyzer like the TotalPhase devices (I have one I got really cheaply), would be the superior choice. But in a pinch, or if you don't have a logic analyzer available, I could certainly see using a scope for protocol decoding.

And of course where you need mixed signal ability of say the SPI input to a DAC and the analog output from the DAC, but probably not on a 2-channel scope ;)

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