On 4/10/2017 3:47 PM, toftat@cowshed.us wrote:
> As I am currently pulling my hair out over this, I figured I'd access
> the hive mind.
>
> tl;dr SPI is not working, I suspect mainly because I have no clue as to
> what I ought to be doing with resistance and capacitance. I am seeking
> some guidance from those who've been successful
>
> I am a hobby-ist making some LED lights for my dock, I have posted about
> problems communicating with the NRF24L01 module previously but that was
> mainly higher level. I am currently finding problems with the hardware
> aspects of SPI. While I think I have the code doing what I expect I am
> seeing some strange behaviour. The SPI is brought out to a header where
> I connect it via 20cm of dupont wire to a breakout board so I can
> connect my bus pirate into the circuit. As I am testing I have my 'scope
> attached to the connector instead of the NRF (looping ground to MISO)
> when I probe /CS, I see a nice mostly square wave from rail to rail
> (0-5v), there is a little ripple on the switching. When I probe the
> clock and the MOSI lines, they are not reaching the 5v rail, it seems to
> be around 1v, and very noisy which I am assuming is causing the bus
> pirate to multiply by 2 (ie I send 0x41, and receive 0x82) I have tried
> the bus pirate in logic probe mode and it only detects the /CS line not
> the clock or MOSI. It feels like these lines are open drain and need
> pull ups, although everything I have read indicates SPI does not need
> this.
>
> Are there any other simple conditioning tricks I might try here? What
> are best practices for SPI? I can post the code, the circuit, and even
> take a picture of the 'scope trace if you'd like. This is really the
> last part of the project before installing everything onto the dock.
>
> Thanks for any input
>
> Anthony
Anthony,

Which microcontroller are you using?

Richard

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