SPI Bus Problem Solved

SPI_Protocol_Decode SPI_Protocol_Decode

This image is the result of a week of pulling my hair out. It is a simple read of a register on a device connected to a micro controller over an SPI bus. The protocol was simple, the code driving it was simple, but until today it refused to work. I had checked the connections, the component values, changed some of the hardware but wasn’t having much luck.

The time came to get it onto the oscilloscope. I treated myself to a Rigol DS1054Z a few months ago and it has proved its worth already. Having access to a 4 channel scope with protocol decoding has allowed me monitor the bus and find my fault. The scope revealed that the SPI MISO line was signalling the same as the SPI Clock. It turned out I had a tiny solder bridge between some header pins on a break out board, never would have thought to look there. After removing the solder bridge I now have a working SPI bus. Now time to do something with it.

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