Negative Voltage on Boot Pin

[derekpickell]

Hello,

Let me know if this is not the best place for this question and I will move it! Haven't gotten any feedback on the sparkfun forum so thought I should try here:

I noticed that the bootloader circuit temporarily drives the BOOT pin to -3.3V. Nowhere in the Apollo3 datasheet do I see any mention of being able to expose pins to negative voltage, and yet the boards seem to work fine! Just looking for confirmation that this is OK. Thank you!

[nseidle]

RedBoard-Artemis bootloader circuit:

Can you share a screenshot of the measurements you took? I remember doing the testing of the BL circuit and I never saw a negative voltage.

[derekpickell]

Here's how I setup my breadboard:

Since I'm planning on uploading code only via a USB to Serial converter, I haven't included the DTR bus (although it's the same circuit), and the RESET is represented by the switch.

Here's the oscilloscope photo: the negative spike is when I manually ground RESET, and the positive is when I unground it.

Really appreciate the help!