Good Results Using MSO-19 USB Scope for SPI

A client was having trouble initializing an SD Card in SPI mode.  They had a nice Agilent scope to look at the signals.  I could put it in single-trigger mode with a slow sweep rate and then turn up the sweep rate (reduce μs per division), effectively zooming out.  Then I could look at the data lines at every clock edge, write down the bits, translate to HEX, and work out what commands and arguments were being sent.

I purchased a $250 MSO-19 USB scope and had good results with it.  As long as a I set a reasonable sweep rate, the SPI decode feature would automatically turn the signals into HEX for me.

Pros:

  • Automatically transcribes input and output data to HEX
  • You can trigger on certain bit sequences or on any input’s rising/falling edge.  This makes it easier to isolate the area where you want to read the data.
  • Easy to send screenshots to colleagues
  • $250

Cons:

  • There was some flakiness that temporarily prevented it from decoding the SPI data.  I had to restart the software and change the sweep rate to get it going again.
  • If you set the sweep rate too low, it won’t be able to read the data.  If you set the sweep rate too fast you won’t get much data, and you cannot scroll.

This was my first time using a USB scope.  The software interface is a little too difficult and sometimes flaky for it to replace a traditional scope.  I am definitely keeping it, though, for its portability data decoding ability.

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