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AnsweredHot!My CAN MCP25625 SO pin is not working properly

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sunnysimon
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2019/07/24 11:07:41 (permalink)
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My CAN MCP25625 SO pin is not working properly

I am reading a register from CAN MCP25625. From data sheet I know SO pin should have no output until I send both command and register address.
 
However, the SO pin sends back something same time as I send address. What might cause this kind of problem?
 
Thank you
 
Simon
 

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mbrowning
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Re: My CAN MCP25625 SO pin is not working properly 2019/07/24 12:53:30 (permalink) ☼ Best Answerby sunnysimon 2019/07/25 06:29:18
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It looks like crosstalk from SDI to SDO - probably through the logic analyzer wires. Everytime SDI goes high, SDO glitches briefly high. I think it's just an artifact. You might put a scope on the signal and see if it's more than that, or set the logic analyzer threshold higher and see if it goes away.
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sunnysimon
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Re: My CAN MCP25625 SO pin is not working properly 2019/07/24 13:02:45 (permalink)
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Thank you mbrowning.
 
Before I use MCP25625, do I need to initialize it before using? If so, are there any specific value I need to use?
 
Simon
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mbrowning
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Re: My CAN MCP25625 SO pin is not working properly 2019/07/24 14:49:07 (permalink)
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Sorry I’m not familiar with that part. I just know what can cause probing issues
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ric
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Re: My CAN MCP25625 SO pin is not working properly 2019/07/24 15:49:03 (permalink)
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mbrowning
It looks like crosstalk from SDI to SDO - probably through the logic analyzer wires. Everytime SDI goes high, SDO glitches briefly high. I think it's just an artifact. You might put a scope on the signal and see if it's more than that, or set the logic analyzer threshold higher and see if it goes away.

Agree, it's probably crosstalk. You need an anlog scope to see what the signal is really doing.
It may be indicating an impedance mismatch, or bad wiring.

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alex88
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Re: My CAN MCP25625 SO pin is not working properly 2020/01/16 12:31:37 (permalink)
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Did you sort this out in the end? I'm having a similar issue. In your case, it looks like the CS line isn't being driven correctly. It should be low while communicating with the MCP25625 and rest high otherwise. 
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