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By robin_hodgson
#209297
I am looking at the Artemis schematics and comparing them to the board on my desk. They don't match up when it comes to the generating the BOOT signal. The eagle schematics for the Artemis Redboard, Nano, and ATP show that one of the resistors is "DNP", which I assume means "Do Not Populate", while the other is listed as being 220K. The cap is shown as a 0.1 uF.

In contrast, measuring the components on my Artemis blackboard shows a 100K resistor in the DNP position, a 10K resistor in the 220K position, and a 2.2 uF cap instead of a 0.1 uF cap.

To add to the mystery, I found a PDF schematic of the Artemis Nano on the Sparkfun website that shows the circuit with a 100K R, a 10K R and a 2.2uF cap. That is not what the Eagle schematic shows for that exact same board, but it does match the components I found on my blackboard.

Which version is correct? Is there documentation on how the BOOT circuit is supposed to work? I could not find any, but when BOOT is one of the search terms it gets a lot of hits...

I have attached a PDF of what I am talking about with snippets from both versions of schematics.
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#209376
Hi Robin,

The discrepancy here is simply due to the fact that the BlackBoard Artemis was being actively developed in both hardware and software. Primarily, that circuit helps with timing for RESET and BOOT for the bootloader and as the engineers worked on the SparkFun Variable Bootloader (SVL) they tweaked that resistor/capacitor circuit to help optimize the timing between reset and the boot pin triggering the bootloader.

On the RedBoard Artemis, that circuit has been optimized to work well with both the Ambiq and SVL bootloaders. As for the Nano, I cannot find the schematic you are looking at but the one on the product page will be the correct one. If you can track down the page you found the odd Nano schematic, that would be helpful for us to find and correct it with the most up-to-date version. Most likely, the schematic is for the retired BlackBoard Artemis Nano.

Finally, in regards to how the BOOT circuit is supposed to work, the best documentation I could find quicky is the Artemis Integration Guide. Both engineers who are the primary developers for all things Artemis are, unfortunately, out of the office this week so I cannot ask them directly but I will ping them to see if they can provide more information about that circuit or know where to point you.

I hope this helps clear up confusion about that resistor/capacitor circuit and gives you some tips on where to go to learn more about the BOOT circuit.
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