Arduino Due spi_readwrite.ino anomaly, CS driven low with no clocks

Projects Networking, Protocols, and Devices
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Hello Arduino Forum,

I am a long-time Arduino fan, owning several Unos, Megas, and now I am working with Due's (which I have two at this time). I have been using an UNO programmed as an SPI slave to test some SPI code I've been developing for a project I work on... But I now need a 3.3V slave and I was hoping to bring up the code on the Arduino due.... Well that is not the topic of this issue.

My first step was setting up SPI Master on Due and hooking up my logic probe... I have a real Saleae Logic which my company purchased for me, but I also have been using the cheap knock-offs you can get from Amazon. For probing SPI comm I found them useful.

So I hooked up the probe for SPI and configured the pins. I am using the default CS of pin 10 and the 'spi_readwrite.ino' sketch... What I notice which is ODD is that the CS is mysteriously driven low before the 32 byte readbuffer...

Here is a screengrab of the logic probe...

image
image330×585 6.87 KB

Is this a bug, is this something which is known and should be documented? I have not seen this on the Uno boards... I am driving my Uno slave at this time with the Excamera labs SPIdriver gadget which I also find to be VERY handy for debugging SPI issues.

Thank you,
Michael Uman
Sr Firmware Engineer
Cana Technlogy

2

I guess that the pin is configured as an output before driving it high. But that's no problem as there are no clock cycles during the CS low phase. No SPI device will have a problem with that, given it acts according to the standard.

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