Comet+ Prototype Boards Are + IN and I'm Hacking!
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SPI MISO Problem

Posted on June 21, 2012 in Category: Blog - 0 Comments

I've been unable to read any of my SPI devices. I think I've isolated the issue to the MISO line which is what the slave devices use to send data back to the microcontroller. I soldered up a new prototype board with just the microcontroller and supporting circuitry to flash the bootloader and upload a sketch. (Sidebar: incidentally, the bootloader is flashed using the SPI lines but in this case, the MCU is the slave instead of the master)

I then wired up a flash chip (which I have working on the Arduino breadboard) to the breadboard on the Comet. Same behavior, which is that it appears that the MISO line is being held low or low enough during transmission to push back faulty data (usually the equivalent of 0, which would indicate the data is LOW). I have reviewed my traces and they look fine, but something is definitely interfering.

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