Author Topic: How do I decode 3 wire, 7 bit SPI on an MSO5000 ?  (Read 390 times)

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Offline LinuxGuy123Topic starter

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How do I decode 3 wire, 7 bit SPI on an MSO5000 ?
« on: January 24, 2025, 12:17:34 am »
I'm reverse engineering (troubleshooting) an odd ball circuit.  The communication busI am looking at is 3 wire SPI, ie half duplex and the data is 7 bits, not 8. 

The communication circuit has 3 wires: clock, data and chip select.  There are 2 node: master and slave.  The master generates the clock and chip select.  The master sends a series of 7 bit words with CS low, then puts it high so the slave can respond, on the same wire.  How would one decode this on an MSO5000 ?

I'm guessing that I am going to need to store the waveform for a communications even, download it to my PC and process it manually.  Am I correct ?
 

Offline thm_w

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Re: How do I decode 3 wire, 7 bit SPI on an MSO5000 ?
« Reply #1 on: January 24, 2025, 01:46:56 am »
From the user manual:

Data Bits:
Quote
Press More -> DataBits, then rotate the multifunction knob or use the pop-up numeric keypad to set the number of bits in the serial data string. The number of bits in the string can be set to any integer ranging from 4 and 32.

Did you do that?
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Offline LinuxGuy123Topic starter

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Re: How do I decode 3 wire, 7 bit SPI on an MSO5000 ?
« Reply #2 on: January 24, 2025, 01:58:45 am »
Nope.  Thanks for the tip.

I was wondering how to set the word length.   
 

Offline LinuxGuy123Topic starter

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Re: How do I decode 3 wire, 7 bit SPI on an MSO5000 ?
« Reply #3 on: January 24, 2025, 07:41:39 am »
Update

The MSO5000 did very well on this task.  I was blown away by how I could tailor the setup to exactly what I needed to see.  Running the scope on my desktop via VNC was a game changer, though it would be nice if the display area on the desktop was bigger.  All in all a very nice debugging session.
 
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