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Topic: Will 3.3V for a ATMEGA16U2 allow it to create a PC compatible USB port? (Read 571 times) previous topic - next topic

JoeN

The ATMEGA16U2 can be run at 2.7-5 volts.  3.3 volts seems like a very nice level because if I run at 3.3 volts it will be compatible with other parts that I want to run.  But does this allow the ATMEGA16U2 to create a true USB port? USB is a 5 volt technology.  The whole point of having a ATMEGA16U2 on this board is to run the Arduino bootloader on it and make the board look like an Arduino Mega R3 to the Arduino desktop software for programming ease and debugging print capability.  I am working off this schematic, I just want to run at 3.3 volts instead of 5.  Can I do that?

http://arduino.cc/en/uploads/Main/arduino-mega2560_R3-schematic.pdf

Thanks.
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majenko

USB provides a handy power connection which, yes, is at around 5V.  USB itself doesn't "run" at 5V.  USB is a "Low Voltage Differential" communication system.  It uses small voltages which swing around a central voltage - around 2¼V if memory serves me right (but it probably doesn't).  One line uses a positive change in voltage for a mark, and a negative for a space, and the other line uses a negative for a mark and positive for a space.

All the USB peripherals I have used have either run at 3.3V, required an external 3.3V regulator to power the USB portion of the chip, or had an internal 3.3V regulator inside the chip to run the USB portions.

Yes, 3.3V will be fine for USB.
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bobthebanana

Take a look at the datasheet, it talks about different methods for powering the thing if I remember correctly. Various voltages, powered from USB, powered from external source, etc.

JoeN


Take a look at the datasheet, it talks about different methods for powering the thing if I remember correctly. Various voltages, powered from USB, powered from external source, etc.


I did scan the datasheet and I couldn't find anything that said the USB portion of the chip operated differently when the chip was run at different voltages.  Again, I was just searching on USB through the datasheet, I didn't read the whole thing as the actual datasheet is 300 pages long.  Just soliciting an expert opinion here.  I guess if the USB doesn't end up working I can still use the board via the programming port.
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bobthebanana

Yeah, it should work. Take a look at section 20.3 for proper connections

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