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3V3 to 5V SPI link


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#1 backseatdriver

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Posted 02 March 2015 - 03:33 AM

I have an old 68HC11EVB that I want to communicate with from my nd+2 via SPI... 

 

1)  What's a good way (following GEP of course) to deal with the 5V / 3V3 difference? 

2)  Is it true that the nd+2 can't operate as an SPI slave? 

3)  Anyone know of a similar project that I can reference? 

 

Thanks in advance.

 

bsd



#2 Mario Vernari

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Posted 02 March 2015 - 04:49 AM

1)  What's a good way (following GEP of course) to deal with the 5V / 3V3 difference? 

 

What is "GEP"?

As for what is supplied by the HC11, the Netduino (by means the MCU) is 5V tolerant so there's no problem.

As for what is supplied by the Netduino (3.3V), the "HC" voltage levels (68HC11) are able to recognize the logic high at 3V: again, no problem.

 

2)  Is it true that the nd+2 can't operate as an SPI slave? 

 

Yes, that's true. You can only try using the Netduino as master and the HC11 as slave.

 

3)  Anyone know of a similar project that I can reference?

 

 

I'm not aware about similar projects, but (under the 2' answer context) should be pretty similar as you connect an Arduino.

 

Question: why don't you use the UART? It's much more convenient if you want exchange data between MCUs...


Biggest fault of Netduino? It runs by electricity.

#3 backseatdriver

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Posted 03 March 2015 - 09:41 PM

Mario, thanks for the response.

 

 

What is "GEP"?

Sorry... GEP in this context means 'Good Engineering Practices'.

 

 

As for what is supplied by the HC11, the Netduino (by means the MCU) is 5V tolerant so there's no problem.

As for what is supplied by the Netduino (3.3V), the "HC" voltage levels (68HC11) are able to recognize the logic high at 3V: again, no problem.

Sounds good.  I was hoping something simple like this could be done.

 

 


Question: why don't you use the UART? It's much more convenient if you want exchange data between MCUs...

 

Originally, I thought I might have a dual master SPI system where both the nd+ and the hc11 shared some SPI slave devices.  With both MCUs on SPI, it made sense to try to use it for communication between MCUs too.  But, because there's no slave mode on nd+ it doesn't sound like such a good idea now.

 

Thanks again for the help.

 

 



#4 Mario Vernari

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Posted 04 March 2015 - 04:27 AM

Fine.

Just forgot:

  • connect the ground between the two boards (EVB and Netduino) before any other wire.
  • keep the wires as shortest as possible.

Have fun.


Biggest fault of Netduino? It runs by electricity.




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