It was a 16f1823, using the hardware SPI. After sending the email I decided
to take it all apart and reconnect everything (hardware version of turning
of and back on again) and as I disconnected the bus pirate the lines  jumpe=
d
up to 5v swings. So I figured that the culprit must have been the bus
pirate, I did not go back to it, and read the bus on my 'scope, one
transaction at a time. There is a little ringing on the lines, but it
appears to be working and I have moved on to making them talk to each other=
..

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
Richard
Sent: Thursday, April 13, 2017 21:44
To: piclist@mit.edu
Subject: Re: [EE] Problems with SPI requirements


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