pin order of atmega32u2 doesn't make sense?

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#1
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Hi! What is the sense in that Atmel makes it hard to connect a Atmega32u2 with a USB connector, If you want to have both parts on one side of the PCB?

You have to use Vias to connect them then.

Last Edited: Wed. Jan 18, 2017 - 09:33 PM
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Are you sure you do not have one of your parts reversed? I am going to have to look at a board I made as I have both on the same side and I don't think I have any vias.

Jim

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They do appear to have different pin ordering in the datasheet, but micro USB connectors are available in both orientations. Perhaps they at first designed it one way and found the opposite orientation ended up being preferred? Just a wild ass guess. Either way, you should be able to find an appropriate part for either chip if you don't want to run vias.

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Yes the pinout is correct, it's shown in this document on page 2, Fiugure 1-1.  http://www.atmel.com/Images/7799...

Yes, you can get "reverse mount" USB connector, even though they are rather rare and more expensive.

It's just unnatural to have the pin order reverse in comparision to the USB connector, so I have no clue what Atmel had in mind designing this.

 

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Granted you have to really go looking for them, but they're not that much more expensive.  Here's 50 for 7 bucks

Last Edited: Thu. Jan 19, 2017 - 12:19 AM
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I just looked and the pins are different as noted already.  I did have to use a couple of vias for the power lines but in my case the D- and D+ lines went right to the connector.

 

 

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Krümelmonster wrote:

Hi! What is the sense in that Atmel makes it hard to connect a Atmega32u2 with a USB connector, If you want to have both parts on one side of the PCB?

 

But if they did it in the other way then people who wanted the connector on the reverse of the board would complain.

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You're required by law to be drunk while deciding the pin layout of integrated circuits.

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Maybe they did the U4 version soon after people started pointing out to them how inopportune the U2 version was in this regard?

 

Chip makers usually don't care about the ease of designing a circuit board around their chip designs.  That's why PCB vias were invented.  Plus it might have been impossible or difficult to get a specific signal to a specific pin given the actual topology on the silicon die.  The pins of the IC are connected to silicon die internally by little gold wires.  Maybe the internal wires would have overlapped had the pins been laid out for ease-of-connector-access in the U2 version.

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@Simonetta, ye, I don't know if that's true but it sounds plausible.

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If you google up a picture of the Teensy board, you will see that the USB connector is on the same side of the board as the chip, and it is "upside down", with the wider edge of the connector at the top.  I don't know how many layers the board has, but at least two.  The tracking from the connector to the chip all appear to be on the top (visible) layer of the board - same side as the chip.

The Teensy-2 (the one I have) uses an ATMega32U4 8-bit uController.

Last Edited: Sat. Jan 21, 2017 - 08:35 PM
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@armstack As the picture of the pinouts in my original post show, the Atmega32U4 isn't the problem. It's the 32U2 that has the "unnatural" pin order.

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Atmega32u2 USB interface pinout is suitable for dongle-style design with Type A onboard USB connector