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Basic Electronics » constant system reset

March 23, 2010
by treymd
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Frustrated. I soldered the MCU up with the required crystal, capacitor, and power connections and uploaded the bootloader with my AVRISP. but when I turn it on it is constantly dumping "abababab..." to the uart.

I'm assuming this is because it is constantly resetting itself, right? pretty sure the bootloader outputs that string to the uart on startup.

I do have pin 1 tied to vcc and 14 to ground. I do NOT have the extra small capacitors tying the crystal to ground. I am using Atmels AVRStudio to program the MCU and it won't set the EFUSE to 0x00 it sets it instead to 0xF9, I'm assuming there is something avrstudio does not like about 0x00.

any thoughts?

March 23, 2010
by bretm
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It starts with 'b' when it boots, and then emits 'a' right before it jumps into application code, skipping the bootloader. It either thinks pin 14 isn't grounded, or the bootloader was compiled without BOOTLOADER_JUMPER or BOOTLOADER_CHAR defined. And if there's no application loaded it could jump right back into the bootloader and do 'b' again, repeating the cycle.

What's the supply level? Could you be running into the brownout detector logic?

March 23, 2010
by treymd
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I'm a noob, I put a switch in there and soldered the ground to the switch but never ran pin 14 to it!

Good info on the boot sequence, that's great to know!

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